影响化学反应速率的因素很多，某课外兴趣小组用实验的方法研究反应速率的有关问题。

（1）实验1 探究Mg与盐酸反应速率的变化规律

取一段镁条，用砂纸擦去表面的氧化膜，铜丝缠着镁条伸入装置甲中，使镁条浸入锥形瓶内的体积为2L稀盐酸（足量）中。镁条和盐酸反应生成H₂的体积与反应时间的关系曲线如图2所示。

① 从图2中看出0-6min内平均反应速率最快的时间段是    。（填代号）

A．0-2min   B．2-4min    C．4-6min

② 请计算4-6min 时间内，用HCl表示的平均反应速率为________。（假设图2氢气体积均已换算为标准状况下的体积，且溶液体积变化可忽略）

③图1装置甲中与镁条相连的铜丝若一起浸入稀盐酸中对反应速率影响下列说法正确的是

A．加快反应速率但生成氢气的总量不变     B．减慢反应但增大生成氢气总量  

C．不影响反应速率                        D．加快反应速率但生成氢气的总量减小

（2）实验2 探究酸浓度对MnO₂与H₂O₂反应速率的影响

已知MnO₂+H₂O₂+2H⁺   Mn²⁺+O₂↑+2H₂O，现取等量MnO₂和下表有关物质，在相同温度下进行4组实验，分别记录收集20．0 mL氧气所需时间。

②有同学提出实验I不可作为实验Ⅱ、Ⅲ、Ⅳ的对比实验，其理由是           。

③若实验测得t₂>t₃>t₄，则可得出的实验结论是                       。

In the United States, older people rarely live with their adult children. But in many other cultures children are expected to care (1) their aged parents. In some parts of Italy, the percentage of adult children who (2) with their parents (3) 65 to 70 percent. In Thailand, too, children are expected to take care of their elderly parents; few Thai elderly live (4) . What explains these differences in living arrangements (5) cultures Modernization theory (6) the extended family household to low levels of economic development. In traditional societies, the elderly live with their children in large extended family units for economic reasons. But with modernization, children move to urban areas, leaving old people (7) in (8) rural areas. Yet modernization theory cannot explain why extended family households were never common in the United States or England, or why families in Italy, which is fully modernized, (9) a p tradition of intergenerational living. Clearly, economic development alone cannot explain (10) living arrangements. Another theory associated intergenerational living arrangements with inheritance patterns. In some cultures, the stem family pattern of inheritance (11) . (12) this system, parents live with a married child, usually the oldest son, who then (13) their property when they die. The stem family system was once common in Japan, but changes in inheritance laws, (14) broader social changes brought (15) by industrialization and urbanization, have (16) the (17) .In 1960 about 80 percent of Japanese over 65 lived with their children; by 1990 only 60 percent did-a figure that is still high (18) U.S. standards, but which has been (19) steadily. In Korea, too, traditional living arrangements are (20) : the percentage of aged Koreans who live with a son declined from 77 percent in 1984 to 50 percent just 10 years later. Although most elderly Koreans still expect to live with a son, their adult children do not expect to live with their children when they grow old.

（2）是（）

A.reside

B.recite

C.redeem

D.rebel