Aformal tone is most appropriate to use in ?
e-mails
essays
conversations
friendly letters

Essays

Essays tend to be written in a formal tone for various reasons. These essays are intended to mimic those that professional researchers write as part of their job. These are usually read by researchers all over the world, and therefore, a formal tone is necessary when you do not know your target audience. Moreover, using a formal tone makes it easier for others to understand what you are saying, as the English is standardized.

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.