在下列各句的空白处填入一个最恰当的单词,使句子意思完整,语法正确。 1. I'm afraid to talk with others in English because my_______English is poor. 2. John ran more_______than the others and missed the train. 3. Be careful not to make the same_______in grammar. 4. It's a_______between you and me. Don't tell others. 5. Taking lots of_______in class is very helpful because you can review well after class. 6. To _______with, she spoke too quickly, and I couldn't understand every word.