热能

2. We must know the _____ of other countries, so that they will not think us ill-mannered.

A．customs

B．habits

C．manners

D．hobbies

胎头娩出后首先要做的是

A．向上托胎颈
B．协助胎头复位
C．协助胎头外旋转
D．将胎颈部下压
E．挤出胎儿口鼻内的黏液和羊水

肝藏魂

在坞内抽出螺旋桨轴（尾轴）后，不需进行（）工作.

A.检查轴颈（铜套）、键槽、锥部等

B.检查尾轴承等

C.检查螺旋桨锥孔配合面

D.拉出尾轴管进行检查

The United States government publishes guidelines for appropriate nutrient intakes. These are known as the Recommended Dietary Allowances (RDAs) and are updated regularly based on new research in nutrition. RDAs are suggested amounts of calories, protein, and some minerals and vitamins for an adequate diet. For other dietary substances, specific goals must await further research. However, for the U.S. population as a whole, increasing starch and fiber in one’’s diet and reducing calories (primarily from fats, sugar, and alcohol) is sensible. These suggestions are especially appropriate for people who have other factors for chronic diseases due to family history of obesity, premature heart disease, diabetes, high blood pressure, and high blood cholesterol, or for those who use tobacco.Snacks can furnish about one-fourth of the calorie requirements among teenagers. Those snacks should also provide much of the day’’s allowances for protein, minerals, and vitamins. Sandwiches, fruit, and milk make good snacks for active teenagers. Food from the food pyramid may be part of any meal. A grilled cheese sandwich or a bowl of whole-grain cereal is just as nutritious in the morning as it is at noon. In addition, a good breakfast consists of any foods that supply about one-fourth of the necessary nutrients for the day.

In this passage RDAs refers to________.

A．types of vitamins

B．types of protein

C．types of minerals

D．amounts of energy, protein, vitamins, and minerals