完形填空
Mary loved small animals. One morning while she was walking in the forest, she found 1weak birds in the grass. She took them home and put them in a small cage. She cared them with love and the birds both grew2. They thanked her3a wonderful song every morning.
But something happened one day. Mary left the door of the 4open. The larger bird flew from the cage. She thought that it would 5. As it flew close, she grasped (紧抓) it. She was very 6to catch it.7she felt strange. She opened her hand and looked sadly at the 8bird. Her great love had killed the bird!
The other bird was moving back and forth (来回) in the cage. Mary could 9its great need for freedom (自由). It wanted to fly into the clear and blue10. At once, Mary took the bird 11the cage and let it fly away. The bird circled once, twice, three times…
Mary enjoyed watching the bird flying and singing 12 Suddenly the bird flew13and landed softly on her head. It sang the 14song that she had ever heard.
The easiest way to lose love is to hold it too tight. The best way to keep love is to 15it wings (翅膀).
(b)、 
(d)、CH≡C-CH=CH2(p)的分子式均为C4H4。下列说法正确的是（ ）
