Choose the One Alternative That Best Completes the Statement or Answers

Choose the one alternative that best completes the statement or answers the question.
Solve the problem.
-In a business meeting, every person at the meeting shakes every other person's hand exactly one time. The total number of handshakes for n people at the meeting is given by $$a _ { n } = \frac { 1 } { 2 } n ( n - 1 )$$ Evaluate $a _ { 12 }$ and interpret its meaning in the context of this problem.

A) 132; If 12 people are present at the meeting there will be 132 handshakes.
B) 66; If 12 people are present at the meeting there will be 66 handshakes.
C) 11; The 12th person shakes performs 11 handshakes.
D) 78; If 12 people are present at the meeting there will be 78 handshakes.