这5道英文选择题到底选哪个?

这5道英文选择题到底选哪个?16.Luxun and his works ___ we are familiar with are considered great.A.whose B.who C.which D.that17.___ it will do us harm remains to be seen.A.What B.Whatever C.Whether D.That18.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,comes19.You can contact us by telephone or e-mail,_________ you prefer.A.whenever B.however C.whichever D.whatever20.This is a very useful book.I’ll buy it,_________.A.how much may it cost B.no matter how it may costC.however much it may cost D.how may it cost