how to solve the problem the little boy turned to his father for help.A. Not knowingB. Ha

问题补充：

how to solve the problem, the little boy turned to his father for help.

A. Not knowing

B. Having not known

C. Not having been known

D. Not known

答案：

(答案→)A. Not knowing

B. Having not known

C. Not having been known

D. Not known

解析：考查现在分词的否定做状语，句意是：不知道怎么解决问题，小男孩向父亲求助。The boy和know是主动关系，not发在现在分词前面。选A。