[tex]De finition\ of\ csc\theta=\frac{1}{sin\theta}\\-----------------------\\therefore\ csc\theta=\frac{1}{sin\theta}\to\frac{1}{sin\theta}=\frac{1}{sin\theta}\\\\the\ denominator\ must\ be\ different\ from\ zero,\ therefore\\\\sin\theta\neq0\iff\theta\neq k\pi\ where\ k\in\mathbb{Z}\\\\Answer:\boxed{D}[/tex]
