接种疫苗可以预防多种传染病吗？

等腰三角形中有一个角是70°，则另外两个角的度数分别是（　　）

①70°、70° ②70°、40°  ③55°、55°  ④110°、110°．

A．①②

B．②④

C．②③

D．①④

Questions from 36 to 40 are based on the following passage:Against this background, the WTO faces several daunting challenges. The first is to continue bringing down tariffs on traded goods. Average penalties have fallen steadily since the GATT’s formation but even the most open economies retain lofty barriers: for instance, America still charges a tariff of 14.6% on import of clothing,five times higher than its average levy.Resistance to tariff cuts is pest in agriculture. According to Tim Josling,a trade expert at Stanford University, tariffs and other barriers on farm goodsaverage a crippling 40% worldwide and create distortions that “destroy huge amounts of value”. A new set of global farm talks is planned to start in 1999. At the least,you might think, these could lock in impressive reforms in Latin America and encourage further watering-down of the European Union’s Common Agricultural Policy.But they will prove difficult: squabbles over agriculture almost sank the Uruguay round.

Where do impressive reforms lock in according to the passage（ ）

A．America

B．Asia

C．Latin America

D．Africa

设N₈为阿伏伽德罗常数的值，对反应

（1）CH₄（5）+2O₂（5）═CO₂（5）+2H₂O（l）△H₁=8 kJ/mol

（2）CH₄（5）+2O₂（5）═CO₂（5）+2H₂O（5）△H₂=a kJ/mol，其它数据如表：

化学键	C═O	O═O	C-H	O-H
键能kJ•mol-1	7q8	x	41p	46p

下列说法正确的是（　　）

A．H₂O（g）═H₂O（l）△S＜0，△H═a-bkJ/mol

B．当有4N_A个C-H键断裂时，该反应放出热量一定为a kJ

C．如表中x=

1796+b

2

D．利用反应（1）设计的原电池电解精炼铜时，当负极输出0.2N_A个电子时，电解槽的阳极一定减轻6.4g

向上延伸

需求分析的主要方法是什么？用这种方法进行需求分析的主要步骤有哪些？