A program consists of two modules executed sequentially. Let $$f_1(t)$$ and $$f_2(t)$$ respectively denote the probability density functions of time taken to execute the two modules. The probability density function of the overall time taken to execute the program is given by

A

$$f_{1}(t) + f_{2} (t)$$

B

$$\int_{0}^{1} f_{1}(X) f_{2}(X) dx$$

C

$$\int_{0}^{t} f_{1}(X) f_{2}(t - X)dx$$

D

max$$(f_{1}(t) + f_{2} (t))$$