The verb "to depend" must be used correctly.We recently had a student write, "It seriously depends of the time spent on the exercise."
While the idea is good, the verb "to depend" is a phrasal verb followed by the preposition "on".
The correct sentence is "It seriously depends on the time spent on the exercise."
Phrasal verbs consist of a verb plus a preposition. Changing the preposition is either incorrect, as in the case of "depends on" or changes the meaning of the verb, such as the difference between "look into" and "look after". "Look into" means to investigate, while "look after" means to take care of.
Be careful when using phrasal verbs!