How can you differentiate second and third conditional? please explain in a very detailed way.

The main difference is that you can use the Second Conditional to describe a result that can happen although it is unlikely that it will, while you use the Third Conditional to describe a situation that could have happened in the past had a condition been met.

halibut, flounder, tuna, and trout are all fish. so your first answer is 1.) fish. and since fish is edible, your next answer would be 3). edible

to describe those fishes more thoroughly, some of those fishes live in fresh water, and some of the fishes live in salt water, and that is not a thing that they all have in common. the question is asking what is common with all of the fish, so answer choices 2). fresh water and 4). salt water are not right.