Given the logic$/$circuit diagram below, which of the following expressions is the correct Boolean expression for F$2?$

a$.$

F$2=$ A $+$ B $+$ B$.$C

b$.$

F$2=$ A$\text{'}+$ B

c$.$

F$2=$ A $+$ B $.$ C

d$.$

F$2=$ A $+$ B $+$ C