Find the Exact Value of the Indicated Trigonometric Function of θ

Multiple Choice

Find the exact value of the indicated trigonometric function of θ.
- $\cos \theta = \frac { 2 } { 5 } , \quad \tan \theta < 0$
Find $\sin \theta$

A) $- \frac { 3 } { 2 }$
B) $- \frac { \sqrt { 5 } } { 2 }$
C) $- \sqrt { 5 }$
D) $- \frac { \sqrt { 21 } } { 5 }$