Suggest improvements for the highlighted problem area:
Tremendous quantities of silt settles at the mouth of the river, forming a delta. At one-fifth the size of France, the Amazon delta is the largest in the world. Scientists believe, however, that it is not likely to get any larger. This delta is considered "mature" because it has not expanded beyond the coastline of the South American continent. Three reasons are proposed:
(1) The Earth's crust sinks slightly under the weight of the delta.
(2) The ocean current along the shores carry away deposits.
(3) The estuary banks are eroded by the tidal flood waves.
- Match Subject and Verb -
In our opening paragraph, we find an example of another mismatch of subject and verb:
The ocean current along the shores carry away deposits.
The singular subject current should have a singular verb:
The ocean current along the shores carries away deposits.
When proofreading your writing, make sure the number of a verb matches the number of the subject. A simple way to do this is to cover up the words between them and then inspect the abridged sentence for consistency.