personal computer system is composed of the processing unit, graphics board, and seyboard with reliabilities of $0\mathrm{.}796,0\mathrm{.}875,$ and $0\mathrm{.}893,$ respectively. This is a series system and even if one component fails, the computer will not function correctly. The reliability of his system is:

Select one:

a$.-0\mathrm{.}684$

b$.0\mathrm{.}622$

c$.2\mathrm{.}564$

d$.0\mathrm{.}855$