用如下图所示的滑轮匀速提升重物，那么 [ ] A.ａ方向的拉力最小 B.ｂ方向

企业一般职工的安全生产教育，由企业负责实施，每年进行（）次，每次不得少于学时。

A、一；6

B、二；8

C、一；8

D、二；6

下列各组词语中加点的字，读音全都相同的一组是(    )

A．扎实/军队扎营雏形/橱窗广袤/玳瑁

B．靡费/望风披靡柠檬/盟约愚昧/联袂

C．喷泉/头喷棉花央浼/媒介收拢/垄断

D．钻床/钻牛角尖沪剧/扈从癸丑/诡秘

请你利用所学习的化学知识判断下列表述中，不合理的是 [ ]

A．厨房内发生天然气泄漏时，应先开窗保持通风再打开电排风扇

B．进入干涸的深井之前必须做灯火试验

C．油锅里的油着火燃烧，应立即盖紧锅盖

D．燃着的木条伸入集气瓶中熄灭﹣﹣瓶中一定有CO₂

根据短文内容，从下框的A---F选项中选出能概括每一段主题的最佳选项。 选项中有一项为多余选项。

小题1:                                             

Americans have learnt more about drinks than they were 20 years ago. Now, encouraged by recent studies suggesting that it can cut the risk of cancer and heart disease and slow the aging process, tea is enjoyed by more and more people. Enough fashionable tea houses are appearing to make even longtime coffee drinkers consider changing drinks.

小题2:                                

Tea is found in more places than ever. The Tea Association of the United States reports that from 1990 to 1999, yearly sales of the drink grew to $4.6 billion from $1.8 billion. “Green tea is seen by people as a ‘functional food’” — bringing health beyond food itself, says Vierhile.

小题3:                                

Recently published studies point out that only teas that come from the leaves of the plant Camellia sinensis contain health benefits. Other teas may taste good, yet they do little more than warm up the drinker. But for Camellia sinensis, the evidence is powerful. In a 1998 study, Harvard University researchers found that drinking one cup of black tea a day lowered the danger of heart disease by as much as 44 percent compared with non-tea drinkers, and other studies have suggested that the antioxidants (抗氧化剂) in these so-called real teas can also prevent cancer.

小题4:                                

One such antioxidant in green tea is ECGC, a chemical 20 times as powerful as vitamin E and 200 times as powerful as vitamin C. “When people ask me for something good and cheap they can do to reduce their cancer risk, I tell them to drink real tea,” says Mitchell Gaynor, director of medical oncology (肿瘤学) at New York City’s Strang-Cornell Cancer Prevention Center.

不动产登记的主要凭证有哪些？