Task 1
Directions: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 through 40．For each question or statement there are 4 choices marked A, B, C, and D．You should make the correct choice.
The Earth has a force that pulls things toward itself．We call this force gravity (地心引力)．This is something we live with all the time, and we take it for granted and hardly ever think about it．But it is a most important factor in rocket operation and
What is the most important factor for a rocket to escape from the Earth? ______