If c + xy = c and x is not equal to 0, which of the following must be true?  Choices:	A) x=0	B) x+y=0	C) y=0	D) x<0	E) x=c
c + xy = c --&gt; xy=0. Since x is not equal to 0, thus y = 0.   Answer: y=0.
<result>C</result>
If c + xy = c and x is not equal to 0, which of the following must be true?