A:didn't he
B:wasn't it
C:did he
D:was it
下面不是三角形稳定性的是( )
( 1 )∠B+∠BCD=180°;(2)∠1=∠2;(3)∠3=∠4;(4)∠B=∠5.能判定AB∥CD的条件个数有( )