单项选择题
The basic causes are unknown though certain conditions that may lead to cancer have been（）.
A.conveyed B.identified C.notified D.guaranteed
单项选择题 If I had not been enjoying the work,I（）so much of it.
单项选择题 Our family（）not to exchange Christmas gifts this year.
单项选择题 No ready technical data available,we managed to（）them.
