One of the Solar Instruments on a Satellite Has Three

One of the solar instruments on a satellite has three major parts which must all operate.Two have reliabilities of .7,and the other has a reliability of .9.In case the system fails,there is an identical backup system for each component which kicks on automatically.The overall reliability of the system,including the backups,is closest to:

A) .40
B) .50
C) .60
D) .70
E) .80