They ( work) heard for annual examination
Go here -- http://www.chompchomp.com/terms.htm -- and scroll down and click on Verbs. Read about verb tenses. Then let us know what you decide.
You'll need to proofread your work carefully. I think you mean "hard" not "heard" and there needs to be some word between "for" and "annual," as well as proper punctuation at the end of the sentence.