单项选择题 硅酸三钙的化学简写是（     ）。 A、C3S B、C3A C、C2S D、C4AF

单项选择题 Look at the following parts of a letter. Arrange them in a logical order.    a.     If you would reduce your price to that extent, we will be pleased to place with you an order that will carry us for the rest of this year. b.     We don't deny that we are interested with your products, as you know. c.     We thank you for your Quotation No.134 for your NVR-FM790 Medical Apparatus and Instruments, and we have given it very careful consideration. d.     Hope to hear from you soon. e.     However, we find that we can obtain from another firm a price of 5% lower than that of yours

单项选择题 前言部分主要是说明写作的目的，介绍有关的概念、定义以及综述的范围，扼要说明有关主题的现状或争论焦点，使读者对全文要叙述的问题有一个初步的轮廓。 A、正确 B、错误