Does this sentence make sense grammatically? [closed]

Solution 1:

They both make sense.

In the first sentence, "Humans on Mars" is a single concept, so a singular verb is appropriate.

In the second sentence, "Humans on Mars" is treated as a collection of people, so the plural verb can be used.

I think the second sentence sounds more natural because when you hear the plural word "humans", you're primed for a plural verb. When you then hear the singular verb you have to backtrack and reinterpret the noun phrase.

You can avoid this problem by rearranging the sentence:

One of the most popular subjects of sci-fi has been humans on Mars.