1. They are

Sounds like: their, there

• test tube
• test-tube baby
• testa
• testable
• Testacea
• testacean
• testaceous
• testacy
• testament
• testamentary
• testamentary trust
• testamur
• testate
• testator
• testatrix
• testcross
• teste
• tested
• testee
• tester
• testicle
• testicular
• testicular artery
• testicular cancer
• testicular vein