Which Phrasal Verb would be appropriate to complete the given sentence?

They were, in fact, good friends, but they _________ on a tricky issue.

fell out

The correct answer is Option (3) - fell out

• Fell out: This phrase is commonly used to indicate that two people had a disagreement or argument. In the context of the sentence, even though they were good friends, they had a dispute regarding a tricky issue.
• Fell down: This usually refers to a physical fall to the ground.
• Fell off: This can mean to detach or drop from something, or sometimes indicate a decline, but it doesn't fit the context of a disagreement.
• Fell for: This means to be deceived by something or someone, or to develop strong feelings for someone, which does not apply here.

So, the sentence correctly completed is: "They were, in fact, good friends, but they fell out on a tricky issue."