no matter how many difficulties we have
适当形式填空 
No matter how many difficulties we have,I believe all problems can_______(solve) in the end.
Mobile phones should __________ (keep) off during the meeting. 
Teenagers under 18 must _______________(not  allow) to smoke or drink. 
Many parents think learning from books must  ______________ (put) first,so teenagers should______________ (not encourage) to work part- time.