restate the sentence

Annually, millions of animals suffer and die in painful tests in order to determine

the safety of cosmetics.

First of all, YOU need to give this a try. We are not here to do your work FOR YOU, but to help you get started and/or to check your work for you.

Give it a try and re-post. Then someone here will be happy to help.

A dangling adverb (annually), separated by a comma, is an acceptable but awkward way to start a sentence. Try adding "each year" somewhere else in the sentence, or move "annually" to after "tests" or "die".

I think after "die" is a better choice, since it places the modifier closer to the verb.

Every year, a large number of animals endure immense pain and lose their lives during experiments conducted to assess the safety of cosmetics.