如图，圆O的直径CD过弦EF的中点G，∠DCF=20°，则∠EOD等于（   ）

等腰三角形的底角为50°，则这个等腰三角形的顶角为（  ）

根据短文内容，从A、B、C、D 四个选项中选出一个最佳答案。(共10分，每小题1分)
　Mr. Green works in an office in Chicago1 Saturday, he went to the office to some work. When he got on the elevator, it stopped between the2 .Mr. Green could not get out of the elevator. He started to 3 , but no one 4 him. Then Mr. Green remembered that it was a holiday in America. No one was going to come to work 5 Tuesday.
　　There was 6 for him to do. He had to wait. With nothing to eat 7 drink, Mr. Green slept for most of the time. Early Tuesday morning, his 8 came to work and found the elevator was not working. When the elevator was 9 , Mr. Green came out. He was cold, weak cold, weak, and tired. He had been in the elevator for about sixty-four 10 ! Now Mr. Green says, “I will only use elevators if they have a telephone in them.”

在自然数集N中，被3除所得余数为r的自然数组成一个“堆”，记为，即
，其中，给出如下四个结论：
①                                                          ②若；③             ④若属于同一“堆”，则不属于这一“堆”其中正确结论的个数            （   ）             

能被对象所识别的动作是(   )