A rocket is intended to leave the Earth’s gravitational field. The fuel in tis main engine is a little less than the amount that is necessary and an auxiliary engine, (only capable of operating for a short time) has to be used as well. When is it best to switch on the auxiliary engine?

• A. at take-off
• B. when the rocket has nearly stopped with respect to the Earth.
• C. It doesn’t matter.
• D. Can’t say