问题
单项选择题
The basic causes are unknown although certain conditions that may lead to cancer have been ().
A. identified
B. guaranteed
C. conveyed
D. notified
答案
参考答案：A
解析：
identify“识别，鉴别”；guarantee“保证”；convey“运送；传达”；notify“通知”。题句意为：“虽然导致癌症的某些条件已经鉴别出来，但是根本的原因还不得而知。”