1.A.for                    B.with               
  C.on                       D.as

2.A.stars                 B.sun               
   C.earth                 D.space

3.A.with                  B.from             
   C.under                D.for

4.A.use                   B.live               
   C.eat                   D.get

5.A.again                 B.also              
   C.besides              D.too

6.A.environment       B.space           
   C.atmosphere        D.earth

7.A.across                B.to                 
   C.from                  D.through

8.A.valid                  B.enormous     
   C.various               D.proper

9.A.As soon as          B.As well as     
   C.As much as          D.As possible as

10.A.shown               B.exposed       
    C.faced                D.covered

11.A.but                   B.because       
    C.so                     D.so that

12.A.get                   B.make            
    C.have                  D.do

13.A.earth                B.atmosphere 
    C.space                D.environment

14.A.pieces               B.units                
    C.parts                 D.elements

15.A.receive              B.accept          
    C.bring                 D.catch

16.A.conventional       B.common
    C.general               D.normal

17.A.shifts                B.converts       
    C.modifies             D.varies

18.A.what                  B.which           
    C.that                   D.why

19.A.put up with         B.keep up with
    C.come up with       D.catch up with

20.A.from                  B.than             
     C.as                      D.away