Question

The teacher, ________ that his students have difficulty in English grammar, has decided to give them some further drilling．

1. A.
   knowing
2. B.
   known
3. C.
   to know
4. D.
   being known

Answer 1

A
难。考查非谓语动词。本句的主句是The teacher has decided to give them some further drilling．中间的结构应该是一个可充当状语的分词结构，表示“当老师知道他的学生在学语法上有困难时……”，是主动形式，故用knowing。