15............energy is much safer than nuclear power
A.Sun
B.Sunny
C.Sun's
D.Solar
19.She can't go to the party because she will have to........her little sister
A.look up
B.look after
C.look for
D.look at
21.Tom: "Why don't we go to paris for the vacation?"
     John:"............"
A.That's a good idea
B.I'm glad
C.That's very kind of you
D.No.Thanhk