Either X or A is true. Therefore, either Y or B is true. If X is true, then Y is true. If A is true, then B is true. Either X or A is not true, therefore either Y or B is not true.
True conclusions require valid logic and true premises.
Two more issues require attention. The first is that the goal of writing is presenting your ideas. Even testing situations require you to provide your ideas. Since you are providing your ideas, it is important to make as easy as possible for your reader to grasp your ideas. Your presentation of your ideas makes your reader's task more or less easy.