16._______ adequate preparation,you don’t have much chance o

16._______ adequate preparation,you don’t have much chance of success.
A.After B.Without C.With D.Before
17.Read the book carefully ____ you’ll find lots of information related to our research.
A.if B.of C.for D.while
18.I like climbing mountains _____ my wife prefers water sports.
A.as B.when C.for D.while
19.Why not _____ to Professor Smith for advice?He is an expert in this field.
A.go B.your going C.to go D.you go
20.The kids lay face down on the beach,their backs ____ to the sun.
A.exposing B.exposed C.having exposed D.were exposing