选出最适当的单词填入空格内.
1 Water becomes solid when it (      ) .
a.freezes
b.boils

2 When a person is exhausted, he has (      ) strength left.
a.mush
b.little

3 Her best garment is the red (      ) with lace.
a.dress
b.doll

4 It was cruel of him to make the donkey carry such a (      ) load.
a.heavy
b.light

5 This machine is (      ) because of the defects in it.
a.expensive
b.unsafe

答案：abaab