有几个英语单选求高手告诉.1.Jim put his hands behind his back __ nobody c

有几个英语单选求高手告诉.
1.Jim put his hands behind his back __ nobody could see them.A.so that B.because C.will have D.But 2.The natural world means __.A.trees B.buildings C.trains D.planes
3.Mary will go to Sanya if she ___a five-day tour A.have B.had C.will have D.has
4.If you go to bed early ,you won't feel so____ A.tired B.happy C.late D.interesting
5.We should make the wheels__and they can turn easily A.circle B.circles C.round D.rings
6.The wheels will turn easily ___we make them round A.before B.if C.because D.so that