Final answer:
The most massive main-sequence stars started out as spectral type O, which are also the most luminous and the hottest. Therefore, the correct answer is A. Type A stars, referring to the given choices, but actually spectral type-O stars based on standard astrophysical classification.
Step-by-step explanation:
To answer which type of stars started out on the main sequence with the largest initial mass, we look to the classification of stars based on their spectral type. The most massive main-sequence stars are classified as spectral type O, which are also the most luminous and have the highest surface temperature. Conversely, the lowest-mass main-sequence stars belong to spectral type M or L, which are the least luminous and the coolest. Therefore, the answer to the student's question is A. Type A stars if we are referring to the given choices in the question. However, if we refer to the correct spectral types used in astrophysics, the answer would be spectral type-O main-sequence stars.