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| A．to provide | B．provide | C．provided | D．providing |
The researehers delermine what type of plants the virus can infect(感染) and_________insects can carry the virus.
| A．those | B．why | C．which | D．how |
—Did you get my letter?
—I received one just as I_________.
| A．set out | B．had set out | C．was setting out | D．would set out |
．When she called at his studio, she_________that he had gone to Japan.
| A．is told | B．was told | C．tells | D．told |
．Robert made a call to his parents yesterday afternoon. To his disappointment, _________of them answered it.
| A．either | B．both | C．none | D．neither |
I_________stop by sometime and thank her for all her help.
| A．must | B．would | C．could | D．may |