Dear XX,
How time flies! We haven't got a letter from you about X days. I have been busy with my studies all the time recently and I couldn't afford any free time to say hello to you with a letter until I happen to have little work to do. In fact, I am eager to know how you are getting on with everything. The terminal examination is drawing near. I think both of us should throw ourselves into the most tensional preparation for it and go over what we have learned in this term. I wish that you succeded in your exams!
yours XX