Inportant!!! About my test tomorrow!!!

when i'm studying, I found some questions that I don't understand but tomorrow is my test! (p.s. i'm in F.2 and please don't answer in too...)
Can anyone help me!?

1. My Testbook said that friction is the opposing force between surfaces that slides or tends to slide over each another,   but is that similar to reaction... = ="
2. why the astronauts need to do exercise at space?
3. what are the different between spacecraft, space shuttle and rocket??

And also some practices are i can fill in the blank:

There is a _______ between all objects. It is always _____ and tends to pull the objects towards one another.  (my ans. attractive force, small)

Liquid hydrogen is the most commonly used liquid fuel in rockets. When it burns in air, ___ is formed (my ans. energy)


Thank you for answering the silly question!!