the ____ of a star will determine its lifespan.\na magnitude\nb mass\nc rotation\nd temperature

Brief Explanations:

The mass of a star is a crucial factor in determining its lifespan. More - massive stars burn through their nuclear fuel faster and have shorter lifespans, while less - massive stars burn fuel more slowly and live longer. Magnitude is related to a star's brightness, rotation affects its shape and magnetic field, and temperature is related to its color and energy output, but mass is the main determinant of lifespan.

Answer:

B. mass