15. For any real numbers $a , b$, and $c$ where $a \geq b$, consider these three statements:
$$\begin{array} { l l }
1 & - b \geq - a \\
2 & a ^ { 2 } + b ^ { 2 } \geq 2 a b \\
3 & a c \geq b c
\end{array}$$
Which of the statements 1,2 , and 3 must be true?\\
A none\\
B 1 only\\
C 2 only\\
D 3 only\\
E 1 and 2 only\\
F 1 and 3 only\\
G 2 and 3 only\\
H 1,2 and 3\\