[单项选择]P波与QRS波群完全无关（）
A. 第一度房室传导阻滞
B. 第二度Ⅰ型房室传导阻滞
C. 第二度Ⅱ型房室传导阻滞
D. 第三度房室传导阻滞
E. 高度房室传导阻滞

某单层工业厂房，设置有两台Q=25/10t的软钩桥式吊车，吊车每侧有两个车轮，轮距4m，最大轮压标准值P_max=279.7kN，吊车横行小车重量标准值g=73.5kN，吊车轨道的高度h_R=130mm。厂房柱距12m，采用工字形截面的实腹式钢吊车梁，上翼缘板的厚度h_f=18mm，腹板厚度t_W=12mm。沿吊车梁腹板平面作用的最大剪力为V，在吊车梁顶面作用有吊车轮压产生的移动集中荷载户和吊车安全走道上的均布荷载q。

Because humans are at the top of the food chain, they are particularly vulnerable to the effects of nondegradable (不可能降解的)pollutants. This was clearly illustrated in the 1950s and 1960s when residents living near Minamata Bay, Japan, developed nervous disorders, shaking, and paralysis(瘫痪，麻痹) in a mysterious widespread. Over 400 people died before authorities discovered that a local industry had released mercury(水银，汞) into Minamata Bay. This highly toxic element stored up in the bodies of local fish and eventually in the bodies of people who consumed the fish. More recently research has revealed that many chemical pollutants are harmful to the human beings.
Pollution also has a dramatic effect on natural resources. Ecosystems such as forests, wetlands, and rivers perform many important services for the earth’s environment. They improve water and air quality, provide living places for plants and animals, and provide food and medicines. Any or all of these ecos
A. Pollution
B. Impact of Pollution
C. Affect of Pollution
D. Pollutants