根据题意得，a2-a=0且a-1≠0，
解得a1=0，a2=1且a≠1，
所以，a=0．
故答案为：0．
正常儿坐位发育为全前倾，头不稳定的月龄为（）。
A.新生儿期
B.2～3个月
C.4～5个月
D.6个月
E.7个月
John asked me _____ to visit his uncle's farm with him. [ ]
A. how would I like
B. if or not would I like
C. whether I would like
D. which I would like
