Answer:
a. It changes a verb into a noun
Explanation:
When you add -tion to the word "complete", it changes a verb into a noun.
-tion is a suffix that forms abstract nouns from verbs or even from word stems that may not be identical with verbs - it maybe expressing action, state or meaning.
Suffixes are known to be a letter or group of letters which are added to word endings in order to change their meanings or functions. They are affixes which are placed after word stems.
Option A is the correct answer.
