In order to make myself()in English, I am studying hard.
A. understand
B. understanding
C. to understand
D. understood
若P,Q均为n阶方阵,且p2=P,Q2=Q.又E-(P+Q)非奇异,则______
A. r(P)<r(Q).
B. r(P)>r(Q).
C. r(P)=r(Q).
D. r(P),r(Q)无法比较.
人类全部社会关系的物质根源(或自然和社会既相区别又相统一的基础)是
A. 生产关系
B. 财产关系
C. 阶级关系
D. 生产劳动
He wrote the book in()with his wife.
A. proportion
B. installment
C. correspondence
D. collaboration