A vertical rod of length $l$ is moved with constant velocity$v$ towards east. The vertical component of earth's magnetic field is B and angle of dip is $\theta$. The  induced e.m.f.  in rod is:
• A
$Blv \cot\theta$
• B
$Blv \sin\theta$
• C
$Blv \tan\theta$
• D
$Blv \cos\theta$