若 l 1 与 l 2 为两条不重合的直线,它们的倾斜角分别为 a 1 , a 2 ,斜率分别为 k 1 , k 2 ,则下列命题 ( 1 )若 l 1 ∥ l 2 ,则斜率k 1 =k 2 ; (2) 若 斜率k 1 =k 2 ,则 l 1 ∥ l 2 ; ( 3 )若 l 1 ∥ l 2 ,则倾斜角 a 1 = a 2 ; ( 4 )若 倾斜角 a 1 = a 2 ,则 l 1 ∥ l 2 ; 其中正确命题的个数是( )
A.
1
B.
2
C.
3
D.
4
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