ac>bd

If a>b and c>d , the product of sides must not follow the order of size in original inequalities. Multiplying or dividing both sides by a negative number reverses the inequality.

For example,

4 > 3, -1 >-2, but 4\times(-1) > 3(-2), ture

7 > 3, -1 >-2, but 7\times(-1) < 3(-2) , false

a+b>c+d

This statement is obviously false.

a+c>b+d

Addition of two inequalities of the same order will not change the order of the inequalities.

If a>b and c>d

Add the two inequalities, we get

a+c>b+d

a-b>c-d

This statement is similar to B, which is Not true.

ad>bc

This statement is similar to A, which is also not true.