Which rule is one of the guidelines for writing formally?
a. use double exclamation marks for emphasis.
b. write in incomplete sentences.
c. use slang or "filler" words.
d. use grammar correctly

One of the guidelines for writing formally is to use grammar correctly (D).

You would use double exclamation points for emphasis, write in incomplete sentences, or use slang or "filler" words when writing informally, like on social media. However, these things are not appropriate in formal writing. Instead, you need to make sure to use grammar correctly.

the answer is c, because they are being narrated.

c (: when ulrich considers throwing georg the flask