单项选择题

幼儿餐桌应在进餐前（）分钟清洁消毒

A.30分钟
B．25分钟
C．20分钟
D．15分钟

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单项选择题

患者吸氧的流量为4L/min，其吸氧浓度为（）

A.40%
B．37%
C．33%
D．275
E．25%

Factor endowment: an economic theory that holds that a country will enjoy a comparative advantage over other countries if it is naturally endowed with a greater abundance of one of the factors of economic production.

答案： Factor endowment theory, also known as the Heckscher-Ohlin t...