27. Which of the follwing compounds can exist as pairs of cis-trans isomers?(1)CH3CH＝CH2 (2)(CH3)2C＝CHCH3 (3)CH3CH2CH＝CHCH3 (4)(CH3)2C＝C(CH3)CH2CH3(5)ClCH＝CHCl (6)BrCH＝CHCl
(A)3, 5, 6
(B)2, 3, 6
(C)3, 4, 5
(D)1, 2, 4
(E)2, 5, 6