help the people in the snowstorm in the South made him worried.
A. Not known how to
B. Unknown what to do to
C. His knowing not how to
D. His not knowing how to
网友回答
A. Not known how to
B. Unknown what to do to
C. His knowing not how to
(答案→)D. His not knowing how to
解析：考查非谓语动词。题中缺少主语，从四个选项中看出可用动名词做主语，排除A和B，分词的否定式，not 应放在分词的前面。所以选D。