A:4S1
B:4S2
C:4S2+S3
D:3S1+4S3
My sister _____ the MP5 for a year. But it broke now.
你知道的寓言故事都有哪些,列一列吧!
坐井观天 ____ ____ ____
若方程x2﹣3x﹣1=0的两根为x1、x2,则 1x1+1x2的值为____ .