From condition A, we can deduce the sufficient condition that condition B holds ~ then A is B ~ and B is A ~.

1 Options A and C: These two options belong to the same type. For an inequality symbol, when both sides are multiplied/divided by a negative number, the symbol will change, so "ab & gtBc" and "a>b" cannot be deduced from each other, which is wrong.

For the equal sign ac=bc, this equation holds when c=0, so it is impossible to deduce a=b, but a=b can deduce ac=bc, even if c=0 holds, so a=b is a sufficient condition for ac=bc, and ac=bc is a necessary condition for a=b, so B is chosen.

If condition a and condition b can be deduced from each other, then both a and b are necessary and sufficient conditions ~~

I hope I can help LZ~~ study hard ~ ~