如图，在三角形ABC中，∠ACB=90°，CD⊥AB于点D，则图中小于平角的角的个数为（　　）

春节前，某市一过江大桥上挂了两串彩灯，这两串彩灯的第一次闪亮相互独立，且都在通电后的6秒内任一时刻等可能发生，然后每串彩灯以6秒内间隔闪亮，那么这两串彩灯同时通电后，它们第一次闪亮的时刻相差不超过3秒的概率是（　　）

化简$\frac{x^2}{x-1}+\frac{x}{1-x}$的结果是

在门捷列夫的元素周期表中，从95号的镅(Am)开始，后序的20多种元素均是人造元素。这一科学事实说明                                                  

根据短文内容，选择正确答案。
D
    John sent for a doctor because his wife was ill. He called the doctor and made sure they would meet at five. He arrived at the doctor's at twenty to five. He thought. “It s a little bit earlier. I'll wait for a moment. It's good to keep the time. ”
    Then he stopped his car in front of the doctor's. He looked around and saw a noisy square not far from here. He went there and sat down on a chair to enjoy the last light of afternoon sun and make himself quiet. He saw some children playing and some women talking to each other happily.
    Suddenly he heard a girl crying. He came up to her and asked some questions. Then he knew she got lost. John tried to find out her address and took her home. The girl's parents were very thankful.
    Then John hurried to the doctor's. The doctor said angrily when he saw him “You're late. Why did you keep me waiting for 20 minutes?" John said nothing but one word "Sorry!”