复合式弧焊变压器，当动铁心与固定铁心间的气隙减小时，则焊接电流（）
A.增大
B.不变
C.减小
参考答案：C
When the old man ____ to walk back to his house, the sun ____ itself behind the mountain. [ ]
A. started; had already hidden
B. had started; had already hidden
C. had started; was hiding
D. was starting; hid
收入弹性是指( )。
A．居民收入变动百分比所导致的产品需求变动百分比B．居民收入变动百分比所导致的产品供给变动百分比C．产品需求变动百分比所导致的居民收入变动百分比D．产品供给变动百分比所导致的居民收入变动百分比、
