by Sage Pearce-Higgins Tue Aug 04, 2020 12:22 pm
First of all, I would pay attention to the simple meaning of the sentence. In the problem above, ask the question 'what is it that's returning the water to the atmosphere?', then you might answer 'okay, it's the transpiration, so that must be the subject'. The same goes for the example from the SC book: ask 'what is it that's outweighing the potential cost?', then you might see 'it's the benefit / benefits that's doing the outweighing.' That simple, logical approach will work in most situations.
To go into more detail, know what a preposition is (check the Foundations of Verbal). These short words, in a broad sense, show position and include 'of', 'from', 'on', 'in', etc. When we've got a preposition, we can leave out that phrase to find the subject and verb relationship. Take a look at these sentences and identify the problems:
1) The number of students are increasing.
2) The flowers from my friend is lovely.
If you leave out the 'of students' and the 'from my friend' then you can see that we've got a subject-verb singular / plural problem. That, in a more nuanced way, is what's happening with both the transpiration and benefits examples.