问题
单项选择题
设A、B均为n阶方阵，且AB=0，则下列（）项正确。
A.若RA.=n，则｜B｜=0
B.若A≠0，则B=O
C.或者A=0，或者B=0
D.｜A｜+｜B｜=0
答案
参考答案：A
搜题请搜索小程序“爱下问搜题”
设A、B均为n阶方阵，且AB=0，则下列（）项正确。
A.若RA.=n，则｜B｜=0
B.若A≠0，则B=O
C.或者A=0，或者B=0
D.｜A｜+｜B｜=0
参考答案：A
完形填空。 | |||
| I have a good friend. His name is Paul. I am short, but he is 1 about 180 cm. I have to 2 glasses every day at school because I can't see things well. Paul doesn't need 3 . He doesn't like his subjects. He thinks they are 4 . Last weekend, we were free (空闲的), so we decided 5 a trip to Central Park. After breakfast, we 6 a bus there. There were lots of people in the 7 . We played tennis and watched a dog show. Then we did some 8 .We had some books with us. There are some 9 in the park. We can't eat in the park and we can't put our thing here and there. We stayed there for about three 10 and then went home happily. | |||
| ( )1. A. tall ( )2. A. put ( )3. A. they ( )4. A. fun ( )5. A. have ( )6. A. saw ( )7. A. park ( )8. A. swimming ( )9. A. shows ( )10. A. hours | B. thin B. buy B. it B. interesting B. to have B. took B. library B. cleaning B. drinks B. days | C. heavy C. sell C. them C. boring C. had C. sat C. zoo C. shopping C. rules C. months | D. quiet D. wear D. him D. dangerous D. having D. made D. supermarket D. reading D. animals D. years |