症见胸闷作痛，甚则胸痛彻背，短气，舌苔白腻，脉弦紧，治疗应首选( )A．木香B．陈

完形填空。

China is a large country of agriculture (农业). We all know that there are more than 800 million   1   in China. China starts to   2   the science of agriculture much earlier   3   other countries in the world.   4   people in Europe and America were trying to shoot wild animals and birds for food, farmers in China were   5   the science of agriculture. For example, Jia Sixie, who lived in the Northern Wei period (386-534AD),   6   one of the farming pioneers. After he finished his work in government, he   7   home and spent his time on research into agriculture. He   8   information, did experiments and learnt from the experience of farmers. He wrote a book called Qi Min Yao Shu. The book   9   has 110000 words is about both farming and gardening. This book is   10   to be an important summary (概要) of the knowledge of farming.

( ) 1．A．workers    ( ) 2．A．develop    ( ) 3．A．to         ( ) 4．A．Where      ( ) 5．A．trying     ( ) 6．A．were       ( ) 7．A．left       ( ) 8．A．advised    ( ) 9．A．who        ( ) 10．A．made    B．farmers     B．grow        B．till         B．For          B．working          B．was          B．built        B．improved     B．whom         B．considered C．pioneers     C．choose       C．then         C．While       C．studying          C．came        C．returned    C．collected    C．it           C．kept       D．scientists    D．interest      D．than          D．Because          D．growing       D．be            D．destroyed     D．planted       D．which         D．studied

等差数列{a_n}的前n项和为S_n，若a₁+a₉+a₁₁=30，那么S₁₃值的是（　　）

A．65

B．70

C．130

D．260

一株桃树上能结出“水蜜桃”、“毛桃”、“油桃”等不同品种的桃，采用的繁殖方式应为（　　）

A．扦插

B．压条

C．播种

D．嫁接

如图1所示，AB段是一段光滑的水平轨道，轻质弹簧一端固定在A点，放置在轨道AB上，BC段是半径R=2.5m的光滑半圆弧轨道，有一个质量m=0.1kg的小滑块，紧靠在被压紧的弹簧前，松开弹簧，物块被弹出后恰好能通过C点，（g取10m/s²）

求：（1）弹簧被压紧时的弹性势能；

（2）保持弹簧每次的压缩量相同，让物块的质量在

1

4

m至m之间变化，求物块从C点飞出后在水平轨道上落点的范围；

（3）保持物块的质量m不变，改变每次对弹簧的压缩量，设小滑块经过半圆弧轨道C点时，轨道对小滑块作用力的大小为F_N，试研究F_N与弹簧的弹性势能E_P的函数关系，并在坐标纸上作出F_N-E_P图象．

什么叫燃点？