如图,直线AB与CD相交于点O,若∠1+∠2=80°,则∠3等于( )
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A.100° B.120° C.140° D.160°
∵∠1和∠2是对顶角,∴∠1=∠2=40°
又∵∠1和∠3互补,∴∠3=140°
选C