Which of the following expressions shows the number of 8-character passwords that can be formed using letters and digits if the password must begin with a letter?
A$21 \cdot 36^7$
B$26 \cdot 36^7$
C$26^5 \cdot 10^3$
D$36^8$
A$21 \cdot 36^7$
B$26 \cdot 36^7$
C$26^5 \cdot 10^3$
D$36^8$