1.Scientists are convinced___the positive effect of laughter___physical and mental health.
A.of;at B.by;in C.of;on D.on;at
2.The news shoocked the public,___to great concern about students' safety at school.
A.having led B.led C.leading D.to lead
3.The financial crisis that originated on Wall Street swept the world,thus___large numbers of workers jobless.
A.leaving B.to leave C.left D.have left
4.It raind heavily in the south,___serious flooding in several province.
A.causded B.having caused C.causing D.to cause
5.By far,there are many problems___to be solved.
A.remaining B.remained C.being remained D.to remain
C.C.A.C.A