1．Modern science has given clear evidence ________ smoking can lead to many diseases.
A. what B. which
C. that D. where
[解析]本题考查同位语从句的引导词。从句结构完整，并且对 evidence 的内容起到了补充说明的作用，故应用 that 引导该从句。句意：现代科学提供了明确的证据表明吸烟能导致很多疾病。
[答案]C
2．His writing is so confusing that it's difficult to make out ________ it is he is trying to express.
A. that B. how
C. who D. what
[解析]本题考查名词性从句。句意：他的书写得这么乱，很难弄明白他想要表达什么。what 引导宾语从句，并在从句中作表语。
[答案]D
