试述外照射防护的基本原则和一般方法。

Questions 196-200 refer to the following report and e-mail.
Ms. Megumi Sullivan　　　　　　　　　　　　　　　　　　　　　　　　　　　　　September 4
Vice President
Granziano Steel Company
1119 East 59th Street,
Chicago, Illinois 60637-1513
Dear Ms. Sullivan,
The maintenance expense figures for the Peoria, Deca, Springfield and Chicago plants are as follows:

Paul Horvath, General Manager
To: Paul Horvath
From: Megumi Sullivan
Sent: Wed 9/11 10:29 A.M.
Subject: Deca plant
The report helped me understand the situation at the plant in Deca.
The board of directors will have a meeting next week to discuss renovation plans for the Deca plant. The Deca plant buildings will undergo extensive and costly renovations. Obviously, there is a great deal of work to be done. I’m planning to spend a few days in Deca at the end of this month, and would like to meet you there.
I would like to know what your assessment of the situation is. My secretary will contact you later this week, and let you know the dates when I’ll be there. My secretary will make the travel arrangements for you. Various proposals will be put forward for renovation at next week’s meeting.
If you have any proposals, please send them to me as soon as possible, and I’II ensure that they are reviewed.

According to the report, which of the following is true

A. Mr. Horvath is proposing that the four plants be renovated.
B. The Graziano Steel Company is planning to relocate its local plants.
C. The newest plant had the lowest expenses in the last three months.
D. The Springfield plant had the most affordable maintenance costs for March.