有以下一系列反应，最终产物为草酸。

已知B的相对分子质量比A的大79，请推测用字母代表的化合物的结构简式。

A．____，B.____，C.____，

D．____，E.____，F.____。

阅读表达。阅读下面的短文，根据短文内容回答问题。

    Mr. King was the owner of a large company. One day, he went into his office early in the morning to get ready to go to the airport and left for another city.

    He was leaving his office when Bill, a night watchman, came in. Bill just came off work(下班). After saying "Good morning" to Mr. King, Bill told the owner about his bad dream. Last night he dreamed Mr. King's plane crashed after it took off. Mr. King was surprised to hear this. He decided to go by train.

    Bill's dream came true. That morning the plane really crashed just after it took off. Later Mr. King returned to his office and heard the accident. To express (表达) his thanks, Mr. King gave Bill $5,000. He also gave Bill a letter. Mr. King told Bill that a man like him should be sent away. Bill was surprised and asked, "Why?" Mr. King said, "Go home and read the letter, and you will know why."

    Bill went home and opened the letter in a hurry. After he read it, he became sad. In the letter there was only one sentence — "A night watchman can't sleep on his duty(值班), but you did."

(Answer the following questions with no more than 6 words.)

内质网腔内的分泌蛋白，输送到高尔基体腔内进一步加工，最后释放到细胞外，在这一过程中分泌蛋白通过的生物膜的层数是(　　)