Final answer:
The phrase "discourage sb from sth" means to persuade someone to avoid a particular action, matching option a) of the given choices.
Step-by-step explanation:
The phrase "discourage sb from sth" means to persuade someone to avoid a particular action. For example, if your friend wants to skip school and you tell them about the potential consequences in order to make them reconsider, you are discouraging them from skipping school. The correct answer to the definition of the phrase "discourage sb from sth" is option a) To persuade someone to avoid a particular action.