這5道英文選擇題到底選哪個?

題目：

這5道英文選擇題到底選哪個?
16.Luxun and his works ___ we are familiar with are considered great.
A.whose B.who C.which D.that
17.___ it will do us harm remains to be seen.
A.What B.Whatever C.Whether D.That
18.I don’t know if he ________,but if he ________ I will let you know.
A.comes,comes B.will come,will come C.comes,will come D.will come,comes
19.You can contact us by telephone or e-mail,_________ you prefer.
A.whenever B.however C.whichever D.whatever
20.This is a very useful book.I』ll buy it,_________.
A.how much may it cost B.no matter how it may cost
C.however much it may cost D.how may it cost

解答：

16.D
17.C
18.D
19.C
20.C