I do not favor the way that you say, "contains multiple errors."
Except for misplaced modifiers, which are self-evident, I never refer to something in the original sentence as an "error." It is a "possible error" and it is only helpful if you find that there are options in the answer choices. Then this location becomes a "decision point" and it is your job to determine which of the options is correct.
Many years ago when I started working with the GMAT, I would miss about 4 out of 14 sentence correction questions. This was a problem because I did not miss any CR or RC questions and so sentence correction was holding me back. The reason that I missed these questions was that I had the wrong approach. Now that I have the right approach I rarely miss and SC question any longer.
Here are two things to do:
1) "Slash and Burn" is the Veritas Prep strategy of eliminating the clutter from a sentence so that you can focus on what is important.
You should practice ignoring three things: Extra clauses that have nothing to do with the underlined portion; prepositions of all types; modifiers - UNLESS those modifiers are misplaced.
2) Identify decision points - which are simply differences in the answer choices - and try to match these with the "decision makers." A Decision maker is the portion of the sentence that tells you which option for the decision point is correct. For a singular/ plural verb decision point, the subject will be the "decision maker."
Sentence correction is primarily a matter of focus and if you can focus on the correct things - primarily decision points and decision makers - and if you can ignore the correct things - extra clauses, prepositions, and correctly placed modifiers - then you will be able to have a high degree of accuracy and efficiency.
Here are a couple of articles to help you think about sentence correction.
https://www.beatthegmat.com/sentence-cor ... 69595.html
https://www.beatthegmat.com/mba/2011/01/ ... correction
