English Grammarly Blog gave the following rules that will help us learn how to use Follow up vs Follow-up
a. Follow Up:
follow up functions only as a verb. If you follow up something that has been said, suggested, or discovered, you try to find out more about it or take action about it.
Ex. State security police are following up several leads
As an adjective, follow-up means intended as a response, a reaction, an evaluation, or a reinforcement of a previous action. For instance, you may be called for a follow-up interview if you did well on your first-round interview, or you may receive a follow-up letter if you write a letter of complaint to a company. In medicine, it specifically refers to an examination to monitor previously administered treatment.
Ex. They are recording a follow-up to their successful first album.
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