根据题意得：3-a≥02a-1≥0，
解得12≤a≤3．
故答案为：12≤a≤3．
In the picture you can see a boy swimming. His mother _____ him.[ ]
A. sees
B. is looking
C. is look at
D. is watching
应用有关药物不良反应的研究结果于具体临床工作时，我们主要从哪几个方面考虑？
