Choose the correct verb form for each sentence:

Question

a. Our ability to use language is one of the things that ( sets / set ) us apart from animals.
b. A young couple ( was / were ) arguing about politics and kissing each other.
c. The blood samples on the tray ( needs / need ) testing.
d. Of particular concern in an emergency ( is / are ) an adequate supply of food and water.
e. The candidate and his opponents ( was / were ) on the stage.