Sentence Correction - Subject Verb Agreement

Yesterday's Mock taught me the importance of practicing daily and remembering the rules. Subject Verb Agreement in Sentence correction is easy to do if one has done an intensive reading through out his life. That person will be easily selecting the right answer without even knowing the grammatical rule behind it.
I too got quite success like this. But I believe its important to know the rule also. Because GMAT creators know this and they might tweak with the question. Therefore I am trying to familiarize myself with the rules. Instead of memorizing them, I am looking at them regularly so that they become my second nature. I am posting here one such revision note.

All the best for your journey fellow Bloggers.