HE DIDN'T KNOW HOW TO SOLVE THE PROBLEM HE ASKED HER FOR HELP.A. SI...

9. - DE KT HK2-ANH VAN 9 (2012-2013)
DE KT HK2-ANH VAN 9 (2012-2013)

9. He didn't

know how to solve the problem

he asked her for help.

A. since

B. because

C. so

D. for