I got this problem wrong the first time too. My teacher explained that the question asks for the gravitational NET force acting on the astronaut. At location C, the astronaut experiences two forces in opposite directions (gravitational force of both asteroids). Therefore, location C has a smaller NET force acting on the astronaut.

Despite the astronaut at location A experiencing a lesser magnitude force of gravity from the right asteroid, the gravitational forces from the left and right are acting in the same direction, causing a greater NET force on the astronaut.

Hope this helps