The professor came into the classroom .A. book under armB. a book under armC. book under

问题补充：

The professor came into the classroom, .

A. book under arm

B. a book under arm

C. book under an arm

D. with book under the arm

答案：

(答案→)A. book under arm

B. a book under arm

C. book under an arm

D. with book under the arm

解析：在独立主格结构中，如使用with复合结构，名词前要用冠词或物主代词。