⑴____ A.photo B. box C. clock D. lost
⑵____ A. thank B. think C. thing D. brother
⑶____ A. brown B. know C. now D. how
⑷____ A. food B. good C. school D. room
⑸____ A. blue B. bus C. lunch D. number
一交变电压的表达式为u=100 2 sin(100πt )V,由此表达式可知( )
当病人需要大量输血时,应该遵循的原则是( )