Q.25 Geometrical isomer (text Q3.6)

Which of (a) to (e) is the concise structural formula of 1-butene?

(a) CH3CBr=CHBr, (b) CH3CH2CH=CH2
(c) CH3CBr=CHCH2Br, (d)  CH3CH=CHCH3
(e) CH3CH=C(CH3)2.