Essays / International relations and liberalism and realism [7]

I have an essay due for Friday. the questions include:

a) Liberals are optimistic about human progress, cooperation and peace. What are the reasons given for that optimisim? Do you beleive their argument to be valid?

b) Why do realists place so much emphasis on security? Do you beleive their arguments to be valid? How important is security in World politics?

Please could someone help me with these questions, i have been researching them for over a week and don't feel confident about my findings at all???