Final answer:
The gravity at Valles Marineris on Mars is 0.38 times that of Earth's gravity.
Step-by-step explanation:
The gravity at Valles Marineris on Mars is 0.38 g, where "g" is the acceleration due to gravity on Earth.
Since the acceleration due to gravity on Mars, in general, is 3.71 m/s², it is significantly less than the Earth's standard gravity, which is about 9.81 m/s². Therefore, the correct answer to the question is a) 0.38 g.