—I have been waiting for you so long.
—Sorry, I have been in the library, _______ my friend look for some books.
A.helped | B.helping | C.to help | D.help |
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—I have been waiting for you so long.
—Sorry, I have been in the library, _______ my friend look for some books.
A.helped | B.helping | C.to help | D.help |