题目:
A portable dry chemical fire extinguisher discharges by().
A.gravity when the extinguisher is turned upside down
B.pressure from a small CO2 cartridge on the extinguisher
C.air pressure from the hand pump attached to the extinguisher
D.pressure from the reaction when water is mixed with the chemical
答案:
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参考答案:C解析:直到青春前期性腺及性征不发育,青春期开始的内分泌变化由下丘脑成熟所发动,下丘脑对性激素反馈作用敏感度下降,垂体分泌促卵泡激素(FSH)和促黄体生成激素(LH)增多,性腺、性征开始生长。因此...