Final answer:
The correct phrase to say 'I wake up at a certain time' in Spanish is 'Me levanto a cierta hora', which implies the speaker gets up at a specific time.
Step-by-step explanation:
The phrase you would use to tell someone I wake up at a certain time is b) Me levanto a cierta hora. This phrase directly translates as 'I get up at a certain time' in English. The verbs despertar (to wake up) and levantarse (to get up) are reflexive in Spanish, meaning the action reflects back on the subject. In this case, adding 'me' before 'levanto' indicates that the speaker is the one performing the action.