JEE Math Practice Question

Let a function f : R $$\to$$ R be defined as $$f(x) = \left\{ {\begin{matrix} {\sin x - {e^x}} & {if} & {x \le 0} \\ {a + [ - x]} & {if} & {0 < x < 1} \\ {2x - b} & {if} & {x \ge 1} \\ \end{matrix} } \right.$$ where [ x ] is the greatest integer less than or equal to x. If f is continuous on R, then (a + b) is equal to:

1. A.4
2. B.3
3. C.2
4. D.5