题干
With a lot of difficult problems ____, the manager felt like a cat on hot bricks.
A：settled
B：settling
C：being settled
D：to settle
答案(点此获取答案解析）
D
振荡电路，能产生一定波长的电磁波，若要产生波长比原来短些的电磁波，可采用的措施为( )