There are n points in a plane no three of which are in the same line excepting p points which are collinear. The number of straight lines by joining them is

• A

  _{${}^n{C}_2$}

• B

  _{${}^n{C}_2-{}^p{C}_2$}

• C

  _{${}^{(n-p)}{C}_2$}

• D

  _{${}^n{C}_2-{}^p{C}_2+1$}