Final answer:
The three prepositional phrases are 'for a test', 'before a test', and 'during the test', underlining the importance of good sleep and preparation for academic success.
Step-by-step explanation:
The selected three prepositional phrases from the provided text passages are: 'for a test', 'before a test', and 'during the test'. This selection is based on identifying phrases that begin with a preposition and include a noun or pronoun that is the object of the preposition. In the context of the text, getting a good night's sleep is highly beneficial and is more likely to lead to a great job performance, which correlates with the overall message that cramming all night for a test is not advisable. Furthermore, the advice against eating a big meal before a test and the recommendation to take deep breaths and relax during the test itself align with the focus on optimizing conditions for academic success.