Listen the birds . They every hour. i) chirp, are chirping
ii) chirped, have chirped
iii) chirp, chirp
iv) are chirping, chirp

iv

Explanation:

i cant really explain but you just have to substitute them all in and see what sounds the most reasonable

A

Explanation:

Listen the birds chirp. They are chirping every hour.

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the answer is b. the tracer looks harmless in flight, but the pilot’s bitten lips and white knuckles suggest how dangerous it can be.