题目

The Unexpected Kindness Of A Stranger Yesterday, as I approached the front door of our public library, a white-haired gentleman stepped back to hold the door for me. You see, I have to go everywhere these days with a walker, and folks are 61. _____ (constant) holding or opening doors for me, so this was not unusual. However, I told the gentleman that the door had 62._____ automatic opener, and he did not need to stay to hold it open. He said “Here I thought I would have an opportunity to be 63._____ (help).” At that, I backed up, let the door close, and allowed him to reopen the d当x=________时，分式无意义；当x=________时，这个分式的值为零．