Identify Systems That Do Not Have Exactly One Ordered-Pair Solution $$\begin{array} { l } x + y = - 1 \\x - y = 17\end{array}$$

Multiple Choice

Identify Systems That Do Not Have Exactly One Ordered-Pair Solution
- $$\begin{array} { l } x + y = - 1 \\x - y = 17\end{array}$$

A) $\{ ( 8 , - 9 ) \}$
B) $\{ ( 8,9 ) \}$
C) $\{ ( x , y ) \mid x + y = - 1 \}$
D) $\varnothing$