Take your time and just refer to this. To be frank with you, this is only part of problems encounterd when learning English. Don't be upset or discouraged whenever we study English. Whatever we practice most is what we will become, as said Richard Carlson in the book entitled " Don't sweat the small stuff - and it's all small stuff ".  It is only time that we need for improving our English with consistent efforts, I am sure. So just enjoy learning English.