Answer: Hello mate!
If you have any real number A; you always have that:
A*0 = 0
this means that the product between a number A and zero, is equal to zero, and this is for every number. (note that A can be equal to 0, and 0*0 = 0)
Then if a*b = 0, you know that, at least one of the numbers is equal to zero, and there is possible that both numbers are equal to zero.
And with this information, you can see that the right answer is D.
"if If a • b = 0, then either a = 0 or b = 0, or both."
because:
0*b = 0
a*0 = 0
0*0 = 0
