Which of the following is non-negative?
Choose one:
A) (a-0.9)(a-1)	B) (a+1)(a-1)	C) (a+0.7)(a+1)	D) (a-0.7)(a-0.7)	E) a(a+1)
5-sec approach:   D. (a-0.7)(a-0.7) = (a-0.7)^2. The square of a number is always non-negative.   Answer: (a-0.7)(a-0.7).
<result>D</result>
Which of the following is non-negative?