题干

从一动物细胞中得到两类大分子有机物X、Y,已知细胞中X的含量大于Y,用胃液处理,X被分解而Y不变。X含有化学元素N,有的还含有S,Y含有化学元素N和P,它们与碘都不发生颜色反应,细胞膜上有X而无Y。下列有关X、Y的叙述,错误的是(   )

A:X可能是蛋白质

B:Y的基本组成单位可能是核苷酸

C:细胞膜上的X可能是载体

D:Y只存在于细胞核中

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D

同类题4

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   Mary and her husband Jim had a dog named “Lucky”.Whenever Mary and Jim had friends come for a weekend visit,they would warn their friends not to leave their luggage open because Lucky would steal something from their luggage and he always hid his finds in his toy box in the basement.

    It happened that Mary found out she had breast cancer.She felt she was going to die of this disease.The night before she was to go to the hospital,a thought struck her,“What would happen to Lucky?” “If I die,who will look after Lucky?” Mary thought.The thought made her sadder than thinking of her own death.

    Mary stayed in the hospital for two weeks.Jim took Lucky for his evening walk every day,but the little dog just looked sad and miserable.

    Finally the day came for Mary to leave the hospital.When she arrived home,Mary was so tired that she couldn't even make it up the steps to her bedroom.Jim made his wife comfortable on the bed and left her to sleep.

    Lucky stood watching Mary but he didn't come to her when she called.It made Mary sad.But she felt so sleepy that soon she fell asleep.

    When Mary woke,for a second she couldn't understand what was wrong.She couldn't move her head and her body felt heavy.But panic(惊慌) soon gave way when Mary realized the problem.She was enclothed with a blanket,and with every treasure Lucky owned!

    While she had slept,the sorrowing dog had made trip after trip to the basement bringing his beloved hostess all his favorite things.He had covered her with his love.

    It's been 12 years now and Mary is still living.Lucky? He still steals treasures and hides them in his toy box but Mary remains his greatest treasure.