12×____ =3600。
He has ________ in touch with his foreign friends for many years.
郭嵩焘将去伦敦途中的见闻日记命名为( )
已知，二次函数y=ax2﹣3x+a2﹣1的图形开口向上，并且经过原点O（0，0），求a的值．
