999.You can only be sure of ____ you have at present； you cannot be sure of something ____ you might get in the future.
A.that；what
B.what；/
C.which；that
D./；that
1000.Having checked the doors were closed，and ____ all the lights were off, the boy opened the door to his bedroom.
A.why
B.that
C.when
D.where
999.答案是B；what引导宾语从句，并在从句中作宾语;that引导定语从句，并在从句中作宾语，可以省略。
1000.答案是B；checked后跟了两个宾语从句，第一个从句的引导词that可以省略，第二个that不可省略。
