Which common feature of informal language should be avoided in formal language?

Informal contractions are the short form of a word that and are used while speaking casually. Contractions are not slang but are similar to slang. They are a part of informal writings. Example: he's (he+is), gonna (going+to),etc.

Use of contractions should be avoided in formal writings. Contractions are basically a combination of two words. Hence their use is inappropriate in formal writings.

Hence, contractions should only be used in informal writings and should be avoided in formal language.

Learn more about the topic here:

link

contractions.

Explanation:

your answer would be a verb. because they are "doing something"

she is outspoken and direct