Chia động từ trong ngoặc:
1,She (ask)________ me the same question three times since yesterday.
2,Nam (read)________ when I saw him
3,________ you ________( be ) free next Sunday morning, Mai?
– No. I ________( visit) our grandmother.
4.He (work)________ as a research and development chemist for 10 years, then he retired.