The rule is that the verb agrees with the noun in subject position -- however, if it still sounds awkward, the sentence should be revised. These are right: 'Studies have shown that an asteroid shower was the main reason for the demise of dinosaurs' 'Studies have shown that asteroid showers WERE the main reason for the demise of dinosaurs' The main reason for the demise of the dinosaurs WAS asteroid showers. The main reason I work IS (for) the children The most important thing in my life IS women ( Me too!
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.