A tricky English test

Hmm, let's see...

1. When you apply for a job, you may have to give the names of two references.

A reference is what a referee gives you, so it should be "the names of two referees" and not "references". ;0)

2. A very high percent of payments nowadays are made with credit cards.

I think it should read "A very high percentage of payments nowadays are made with credit cards". Although I don't really like the sentence structure here.

3. Scientists have analysis how animals communicate (maybe I should use the world 'recearches' instead of 'analysis'?)

Maybe you're looking for "Scientists have analysed how animals communicate"? E.g. a verb rather than a noun?

4. Skiers are under great danger if an avalanche occures.

Try "Skiers are in great danger if an avalanche occurs".

Hope that helps a bit! :0)