Several basic areas of the language seem to present outsized obstacles:
Your/you’re
Who/whom
I/me
Here’s an easy test to help with Your (possessive) vs You’re (contraction of the words “you are”).
Quiz Yourself On You’re vs. Your!
Do thine eyes deceive thee? No, this is definitely a quiz on how adept you are at using “you’re” and “your.” Take it and see how well you do!
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