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问题 选择题

属于单细胞的藻类是（　　）

A．衣藻

B．水绵

C．海带

D．紫菜

答案

藻类植物多种多样，有单细胞的，如衣藻，整个身体由一个细胞构成，内有杯状的叶绿体，也有多细胞的，如水绵、海带、紫菜、裙带菜、石花菜等，它们虽然由多细胞构成，但结构很简单，无根、茎、叶的分化．可见A正确．

故选A

单项选择题

暖通空调常用风机选择，下列哪一项是不正确的？（）

A、输送有爆炸危险性的气体时，应选用防爆风机

B、机翼型叶片的离心风机效率高，适用于大型系统

C、前弯叶片离心风机构造轻，运行速度低，多用于低压系统

D、对大流量、低压头的通风系统，不宜采用轴流风机
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单项选择题

A typical (160) language contains an applicative sub-language which approximates the mathematical abstractions of "timeless" functions applied to "spaceless" values, where the actual operation sequences and use of storage space during expression evaluation are organized behind the (161) . In this setting, values are data structures of low volume, typically a few computer words or less, which means that an illusion of spacelessness can be realized by having (162) results during expression evaluation stored at the discretion of the language implementation, and effecting parameter (163) and (164) operations through value copying.

（160）是（）

A.imperative

B.mandatory

C.compulsory

D.voluntary
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