Tom knew nothing about it ( ) his sister told himA since B if C until

问题描述:

Tom knew nothing about it ( ) his sister told him
A since B if C until

C until
not..until------直到。。才;不到。。不;一到。。就

C 与 not ……until 相类似

C
Tom knew nothing=Tom didn't know any thing
not...until...知道...才...