Choose the best answer to complete the blank in each of the following sentences.
Since 1980, scientists in the world ________a lot of things to fight AIDS.
have done are doing did had done Môn học
Chủ đề / Chương
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Chủ đề
Choose the best answer to complete the blank in each of the following sentences.
Since 1980, scientists in the world ________a lot of things to fight AIDS.
have done are doing did had done
