成年人一次献血200～300mL不会影响健康的原因是（ ）
A．损失200～300 mL的血液，对人体丝毫没有影响
B．损失的血细胞和营养成分在不久之后会得到补充
C．少量损失血液有助于健康
D．血液的减少可以促进人体造血
无偿献血是指为了拯救他人生命，志愿将自己的血液无私奉献给社会公益事业，而献血者不向采血单位和献血者单位领取任何报酬的行为．我国鼓励无偿献血的年龄是18-55周岁，男体重大于等于50公斤，女体重大于等于45公斤，经检查身体合格者，都可以参加献血．每次可献血200-400毫升，两次献血间隔期应为6个月．人体内的血量是相对稳定的，成年人的血量为体重的7%～8%．医学研究证明，如果一次失血不超过400ml，血浆和血细胞以及营养成分可以在短时间内通过自身的调节作用恢复到正常水平，因此，一个健康的成年人每次献血200～300ml不会影响身体健康，而且还有利于提高自身造血器官的造血功能．可见B符合题意．
故选：B
December 24 arrived along with a heavy snow. It was my first Christmas Eve without my mother, and the day’s usual 36 had disappeared. The telephone rang. I 37 it and went to my bedroom to bury the continuous 38 , knowing it must be my friend Rebecca calling. How could I be 39 ? I wanted to be left 40 . My heart felt as 41 as the falling snow. 42 can I stop missing my mother? I 43 the window. Seeing Rebecca’s car parked out front, I went back to my bed and drew the covers over my head. “Lucy!” she shouted. “I know you’re in there. Answer the door!” “Leave me alone!” I 44 back. I heard paper rustling(沙沙作响) as she slid 45 under the door. “Merry Christmas, ” she called out. Not answering the 46 made me even 47. It wasn’t fair to my best friend. Her father and sister 48 in a car accident when she was eight years old. 49 , her mother had to return to 50 , and Rebecca was left to look after herself. When she left, I carried the small package, sat down and 51 it. Inside was a golden pen and a journal. When I opened the journal’s front cover, out fell a bookmark with a(n) 52 written on it: Dear Lucy, My words won’t heal（治愈）the 53 . But your own words can. Love, Rebecca As I stared at the journal’s blank pages, a single tear fell on the page which quickly absorbed it. That night, I 54 the phone and dialed her number. “Looks like the snow is melting(融化), ” I said. “Spring was just ___55____the corner.”
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