The professor, ______ whether anyone would come to help him, had

The professor, ______ whether anyone would come to help him, had to prepare for the experiment by himself.
A、did not know
B、having not known
C、had not known
D、not knowing
【正确答案】：D
【题目解析】：句子的谓语是had to prepare for,第二动词应该用非谓语动词。动名词的否定形式是直接在其前加not。答案为D。