We didn’t feel surprised when we found he fixed his eyes on the food with a(n)________expression on his face,for we knew that he hadn’t eaten anything for 3 days.
With his attention________on the shops along the roadside,he knocked an old man down while riding to school.
A concentratingB.concentrated C.to concentrate D.concentrates
答案 B
解析 考查词组,故选B项。