Most of the time, he has no trouble ______________ the people from different countries.
A:understand
B:to understand
C:understanding
设计算法,输出1000以内能被3和5整除的所有正整数,已知算法流程图如图,请填写空余部分:①____;②____ .
下列事件中,不是利用浮力工作的是( )