A:3a+4b=7ab
B:7a﹣3a=4
C:3a+a=3a2
D:3a2b﹣4a2b=﹣a2b
____ (wear) a big smile on her face, she came into the classroom.
戊戌变法的诸项措施中,有利于资本主义发展的( )