用适当的介词填空。
1. I went ______________ a trip.
2. I went ______________ a zoo.
1. on 2. to
下列燃料中发球清洁燃料的是[ ]
A.煤炭
B.汽油
C.氢气
D.柴油
A.boundary value analysis
B.statement testing
C.branch testing
D.path testing