Answer :

Conventions in this sense are "all of these" things. In that they have become accepted in the literary and academic world. Of course this is not always the case with writing, however.

Answer: d. All of these

Writing conventions include spelling, punctuation, capitalization and grammar.  These are some of the most difficult elements to master when writing a text. However, they are also some of the most important. It is necessary to pay attention to these rules in order to make sure that an essay flows well, is understandable, and can be read by a wide audience.