探放老空水时，放水过程中必须遵守的规定有（） A.撤出受水威胁人员 B.定期测定水量

有如下类定义：
class Foo

public：
Foo(intv)：value(v) //①
～Foo() //②
private：
Foo() //③
int value＝0； //④
；
其中存在语法错误的行是( )。

A．①

B．②

C．③

D．④

在验证力的平行四边形定则的实验中，某学生有如下操作步骤，试按合理的顺序将步骤序号填在下面的线上______，其中不完整的步骤是______请补充完整______．

A．只用一个弹簧秤，通过细绳套把橡皮条结点拉到O点，记下弹簧秤读数F和细绳方向

B．把橡皮条一端固定在木板上，在橡皮条另一端栓上两根细绳套（此端交点称为结点）

C．用两个弹簧秤通过两个互成角度的细绳套拉橡皮条，使之伸长到一定长度，在白纸上记下结点位置O，同时记下两个弹簧秤读数F₁、F₂

D．把白纸钉在木板上；

E．改变F₁、F₂的大小和方向，重作两次实验

F．用同一比例图示F₁、F₂和F，作图求出F₁和F₂合力F′，比较F和F′得出实验结论．

为了保证混凝土的可泵性，每立方米混凝土水泥用量不小于（） 。

A.280kg

B.300kg

C.350kg

D.500kg

Questions 81-90 are based on the following passage.

It sounds like a science fiction, but researchers say it’s a scientific fact: Microscopic organisms dubbed "killer algae" are paralyzing fish with unknown toxins and then eating away at their flesh. They might be making people sick, too.
The name given to this single-cell organism, or dinoflagellate, is Pfiesteria piscimorte- literally, "fish killer. " It was discovered at North Carolina State University in 1988, but at the same time, few scientists believed in its existence, much less in its highly unusual predatory nature. But ongoing research has led to international acknowledgment of the phenomenon and, recently, research funding.
Seemingly prompted by an unknown substance secreted by fish, the aggressive creature swims into action. It sends neurotoxins into the water and air, paralyzing a fish’s nervous system, and causing it to gasp for air at the surface. Eventually the fish suffocates. The killer dinoflagellate then attaches itself to the fish and begins sucking away at its flesh. This macabre scenario may help solve several sea mysteries, such as why fishermen report seeing "fish walks" (fish trying to leave the water) and pools of dead fish with holes eaten through them.
Whether humans are affected by the dinoflagellate’s toxin remains to be seen. Researchers think it’s unlikely eating fresh fish are in danger, but anyone with frequent exposure to the creature could be in peril. Several researchers working with the algae have reported bouts of memory loss and disorientation.
To understand the killer algae further, scientists must fully characterize their toxin and determine what stimulates them to attack. They also need to know if the algae are hurting fish populations, and whether pollutants make them more likely to attack.

The word "they" underlined in Paragraph 1 refers to ______.

A. organisms
B. fish

C. toxins

D. flesh

FⅣ是（）。

A.K⁺

B.Ca²⁺

C.Cl^-

D.Na⁺

E.HCO₃^-