听力原文： If there are no more questions about the textbooks or syllabus, I'd like to briefly explain the grading procedure I'll be using in this course. 50% of your grade will be based on the mid-term examination and the final exam. Both of these exams will be given during class time and each will be 2 hours long. In a lecture class of this size, it is impractical and almost impossible to give make-up exams, so plan on being healthy and in class on those days; otherwise, your final grade average may suffer. The semester is 16 weeks long and quizzes will be given every 2 weeks to make sure you're keeping up with what's going on in class. Quizzes will count as 15% of your grade and daily homework will count another 15 %. Homework will be collected and graded by the teaching assistants in your laboratory sessions. So, 50% for exams, 15% for quizzes, and 15% for homework. The remaining 20% of your grade will be based on class participation. I'm obviously not in a position to judge this, but I will ask your teaching assistants to evaluate how actively you participate in their classes. Remember, the purpose of the laboratory sessions is to give you a chance to ask questions about the lecture and to discuss difficult points. When would this talk most likely be given?