37.Tom was about to close the window ______ his attention was caught by a bird.（ ）

A.when

B.if

C.and

D.till

37.A【解析】句意：汤姆正要关窗户，这时一只鸟吸引了他的注意力。固定句式be about to do sth.when…表示“正要做某事，突然…（发生了意料之外的事情）”。故选A。

38.I had great difficulty ______ the suitable food on the menu in that restaurant.（ ）

A.find

B.found

C.to find

D.finding

38.D【解析】句意：我在那家饭店的菜单上很难找到合适的食物。have difficulty （in）doing sth.表示“做某事有困难”。故选D。

39.______you may have，you should gather your courage to face the challenge.（ ）

A.However a serious problem

B.What a serious problem

C.However serious a problem

D.What serious a problem

39.C【解析】句意：无论你有多么严重的问题，你都应该鼓起勇气去面对挑战。however用作连词，相当于no matter how，引导让步状语从句，意为“不管怎样，无论如何”，其结构为“however/no matter how+形容词或副词+主语+谓语”。故选C。