21题为什么选ask about 不选know about,know about 按句意说也可以

21题为什么选ask about 不选know about,know about 按句意说也可以 know of know about know know of know about know,know about,know of know 和know about有什么区别 know和 know about 有什么区别? know about . learn about. 造句 know much about还是know many about know about和know of know,know about,know of有什么区别? know about sth是什么意思? know a lot about