某人的下列细胞中，含染色体最少的是（ ）
A．神经细胞
B．受精卵
C．口腔上皮细胞
D．未受精的卵细胞
A、C、在人的体细胞中，染色体是成对存在的，即是23对．故不符合题意．
B、通过受精作用，精子与卵细胞相融合，受精卵中的染色体一条来自父方，一条来自母方，所以受精卵中的染色体数目又恢复到23对．故不符合题意．
D、在形成生殖细胞的过程中，要进行一种特殊方式的细胞分裂，成对的染色体要两两分开，分别进入两个子细胞中所以，结果使生殖细胞中染色体数目减少一半．故符合题意．
故选：D
A large cat arrived at a farm where many mice lived. None of them dared go outside for fear of being by the cat. The mice decided to hold a to find a way of stopping themselves from being in danger. One day, when the cat was out, mice of all ages into the meeting room. “Let’s build a big trap（陷阱），”one mouse suggested. When this idea was ，another said, “What about poisoning (毒死) her?” But knew where to buy the poison. One young mouse, whose mother had become the cat’s food, angrily said, “Let’s cut her teeth, so she can do no more harm.” But the meeting did not accept his . At last, one mouse, than the rest, jumped onto a table. Waving a bell, he called for silence, “Be quiet！We’ll tie this bell to the cat’s tail（尾巴）, so we’ll always know she is！We’ll have to escape, and the slower and weaker mice will hear her coming and be able to ！” Hearing the words, everyone got and they congratulated him on his good idea. “We’ll tie it so tightly (紧紧地) that it will never drop off！” “She’ll never be able to walk again！Why, the other day, she suddenly appeared right in front of me！Just imagine...” However, the clever mouse said, “We must who is going to tie it on her tail.” There was not a sound in the room. Nobody was enough to put the plan into action. The meeting ended without any decision being made. It’s often very to have good ideas, but putting them into practice is much more difficult.
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