EnglishVod.net>第一部分 句号的用法规则

Rules for Using Periods 

Use a period after an initial and after every part of an abbreviation, unless the abbreviation has become anacronym-an abbreviation that is pronounced as a word, such as AIDS-or a widely recognized name (TV, FBI, NATO, NASA). Titles-Mr., Ms., Dr., and so on-are also abbreviations that take periods. If the abbreviation comes at the end of a sentence, only one period is needed. 

Examples: 
　　The tour leaves on Mon., Jan. 1, at 3 P.M. 
　　The book was written by C. S. Lewis. 
　　A. J. Mandelli researched brain function for the FBI. 

Use a period before a decimal and between dollars and cents. 
 Examples: 
　　A gallon equals 3.875 liters. 
　　The new textbook costs $54.75. 
　　Only 5.6 percent of our consumers spend over $100.00 per month on our products. 

 ·Use a period at the end of a sentence that makes a statement. 
Examples: 
　　Henry Kissinger served under two U. S. presidents. 
　　Wilson will lecture in the forum after school today. 
　　Many consider P. T. Barnum the best salesman ever to have walked the earth. 

Use a period at the end of a sentence that makes a request, gives an instruction, or states a command. 
Examples: 
　　Empty the kitchen trash before you take the garbage out. 
　　Turn right at the first stop light, and then go to the second house on the left. 
　　Use a period at the end of a sentence that asks an indirect question. 
Examples: 
　　My neighbor asked if we had seen his cat. (The direct question was, "Have you seen my cat?") 
　　Quentin wanted to know how we had arrived at that answer. (The direct question was, "How did you arrive at that answer?")