直流发电机的电枢旋转时,电枢绕组元件中感应电动势的().
A、大小和方向都在改变。
B、大小不变,方向改变。
C、大小改变,方向不变。
D、大小和方向都不改变。
参考答案:A
Parents today also worry about their children’s diets. Some doctors give the following advice:
小题1:According to the doctors’ advice ,what does junk food include ?
A.milk and vitamins.
B.Fruits and sugar.
C.Vegetables and salt.
D.Fat, oil, salt and sugar.小题2:In this passage, doctors think that teenagers should eat more ______ .
A.food with no vitamins.
B.fat and sugar
C.vegetables and fruits
D.salt and oil小题3:The best title for this passage is ______ .
A.Bad Habits
B.junk Food
C.unhealthy Food
D.advice on Healthy Eating
简述汽轮机超速试验的目的?