问题
选择题
鸟类体表被覆羽毛，前肢变成翼，能进行“双重呼吸”，体温而恒定。鸟类的“双重呼吸”是指 [ ]
A．呼气和吸气时，肺和气囊都进行气体交换
B．吸气时，在肺内进行气体交换
C．呼气时，在肺内进行气体交换
D．呼气和吸气时，在肺内都进行气体交换
答案
答案：D
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鸟类体表被覆羽毛，前肢变成翼，能进行“双重呼吸”，体温而恒定。鸟类的“双重呼吸”是指 [ ]
A．呼气和吸气时，肺和气囊都进行气体交换
B．吸气时，在肺内进行气体交换
C．呼气时，在肺内进行气体交换
D．呼气和吸气时，在肺内都进行气体交换
答案：D
“Hi, Mom, happy fiftieth birthday!” I heard my son, Brian, say as as if he were sitting next to me. he wasn’t.Brian was on the USS Kitty Hawk on maneuvers (大规模演习) between our U.S. shore and the Persian Gulf. My party-loving friend, Denise, had me out for a quiet fiftieth birthday celebration dinner. When we at the restaurant, I scanned (扫视) the sea of , but didn’t recognize anybody. A wave of washed over me, and tears welled in my eyes when I heard Brian in my head. “Hi, Mom, happy fiftieth birthday.” “What’s wrong?” Denise asked when she saw me dabbing (轻轻擦) at my . “I think I’ve had too much wine. I keep Brian wish me a happy birthday,” I said. She gave me a(n) smile. “Our table is ready,” she said, leading me toward the stairs. I’d hardly sat down in the chair of honor when a entered the room, carrying a sheet of cake. The firefighter the cake on the table in front of me so I could the fifty blazing candles. Once again I heard Brian speak, “Mom, be sure to me a piece of cake.” This time he very far away, but it seemed that he was just in front of me. I in my chair. Was I losing my mind? “I’ll have some as soon as I get this helmet (头盔) ,” the firefighter said. Every drop of blood in my veins flowed to my feet. He his uniform and quickly pulled the helmet from his head. “Brian!” “Hi Mom. Happy fiftieth birthday!”
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