Learn the Grammar Rule You Keep Getting Wrong

Some grammar rules do not stick because they are explained alongside six other rules at the same time. This explains just the one you keep getting wrong: the rule itself, three correct examples, three errors fixed, and a simple test to apply when you are not sure. Narrow and specific by design.

Explain the grammar rule behind [the specific thing I keep getting wrong: e.g. when to use 'which' vs 'that', how comma splices work, when to use a semicolon]. Give me: the rule in one sentence, three examples of it used correctly, three examples of the same error and how to fix each, and one memory aid or test I can apply when I am unsure. Be specific; do not explain every related grammar rule as well.