In English, it is not always necessary to repeat some words. Look at the following examples:
am / is / are / was / were:
Are you nervous? – I wasn’t (nervous) before, but I am (nervous) now. (We do not need to repeat the word “nervous,” since the original question gives us the context.)
I’m not hungry, but Scott is (hungry).
have / has:
I’ve gotten a call from the boss, but Jack hasn’t (gotten a call from the boss). (Again, enough context is provided for us by the first use of “gotten a call from the boss.)
do / does / did:
I don’t like coffee, but my brother does (like coffee).
can:
I can’t make it to the staff meeting, but Tom can (make it).
will:
The weatherman said it won’t rain today. – He’s full of beans. I think it will (rain).
might:
Is Mike coming to the party? – I don’t know. He might (come).
should:
If you haven’t already made a reservation, you probably should (make one).
Notes:
1) Contractions are not possible with positive sentences like these.
I’m not hungry, but Scott is. (NOT: I’m not hungry, but Scott’s.)
He’s full of beans. I think it will. (NOT: I think it’ll.)
I wasn’t before, but I am now. (NOT: I wasn’t before, but I’m now.)
Sally hasn’t seen a ghost, but I have. (NOT: Sally hasn’t seen a ghost, but I’ve.)
2) Contractions are permitted with negative sentences like these.
I’ve gotten a call from the boss, but Jack has not / hasn’t. (OK)
Mary likes pumpkin pie, but I do not / don’t. (OK)
Tom should retire, but he probably will not / won’t. (OK)
Are you…?, Is there…?, Will he…?, etc. questions can be answered with “Yes, I can” / “No, I can’t,” etc.
Are you sleepy? – Yes, I am. / No, I’m not.
Will Jack pick us up at the airport? —Yes, he will. / No, he won’t. Dave will.
Is the store manager on duty? —Yes, he is. / No, he isn’t (he’s not).
Has Father bought Mother a birthday present yet? —Yes, he has. / No, he hasn’t.
Should Billy go see the dentist? —Yes, he should.
Simple present: Use “do / does.”
I don’t like coffee, but my brother does. (i.e., my brother likes coffee)
Becky plays the piano, but Sally doesn’t. (i.e., Sally doesn’t play the piano)
Do you take this bride to be your wedded wife? —Yes, I do.
Simple past: Use “did.”
Did you pick up the dog from the vet? —Oh no, I didn’t! I totally forgot.
Did you and Jack come home early from school? —I did, but Jack didn’t. He had to stay after class.
Did Tom catch the train? —No, he didn’t, so he wound up taking a later one.
Exercise. Complete the following sentences. Use only one verb – is, was, have, do, can, will, might, should – each time.
1. I’m not bored, but Tom _________.
2. Mary can’t keep a secret, but I _________.
3. Mother doesn’t watch the news, but Father _________.
4. Our house wasn’t damaged by the storm, but our neighbor’s (house) _________.
5. Hannah won’t eat peas, but Jacob _________.
6. Will Uncle Kirk come to the graduation? I don’t know – he _________.
7. I can’t make it to the party, but Sue _________.
8. Let’s skip school today. —Do you think we _________? What if Mom and Dad find out?
9. I haven’t been to China, but Sharon _________.
Exercise. Complete the following sentences. Use a negative verb – isn’t, wasn’t, haven’t, don’t, can’t, won’t.
1. Betsy has seen the movie Gone With the Wind, but I _________.
2. Clarice exercises every day, but I _________.
3. Dave is a hard worker, but Mary _________.
4. Dick can ride a bike, but Jane _________.
5. I thought the air conditioning was on, but it _________.
6. Sid likes school, but Tom _________.
7. Ken will sing a solo, but Keith _________.
8. I’m going to the county fair, but Jack and Jill _________.
Exercise. Complete the following sentences. Use do/does/did or don’t/doesn’t/didn’t.
1. Brad doesn’t have a lot of friends, but Roland _________.
2. This brand of laundry soap really gets clothes clean, but that one _________.
3. Bill thought it was a great movie, but I _________.
4. We don’t have a dog, but Dan and Rachel _________.
5. The Fosters have a big yard, but we _________.
6. Emma reads a lot of history, but Ben _________.
7. I don’t know too much about chemistry, but Kathy _________.
8. Mike heard rumors about the company going bankrupt, but Mark _________.
9. Sam doesn’t have any homework, but I _________.
10. Steve didn’t go to Scouts, but Joe _________.