1. They are

Sounds like: their, there

• covalent
• covalent bond
• covariance
• covariant
• covariation
• cove
• covellite
• coven
• covenant
• covenanter
• covenantor
• Coventry
• cover
• cover charge
• cover crop
• cover for
• cover girl
• cover glass
• cover letter
• cover note
• cover plate
• cover point
• cover slip
• cover song
• cover up