五、篇章結構（占 10 分）    Spider webs are one of the most fascinating examples of animal architecture. Themost beautiful and structurally ordered are the orb webs. 66 In order to do so, thethreads of the web have to withstand the impact forces from large and heavy prey as wellas environmental forces from wind and rain for at least a day in most cases.     67 The first is its geometry, which consists of an outer frame and a central partfrom which threads radiate outward. 68 The whole web is in tension and held in placeby anchor threads, which connect the frame to the surrounding vegetation or objects. Thesecond and perhaps most important characteristic is the material with which it is built.Spider silk is a kind of natural composite that gives this lightweight fiber a tensilestrength comparable to that of steel, while at the same time making it very elastic. 69One is highly elastic and can stretch to almost twice its original length before breakingand, for most types of spiders, is covered in glue. 70 The other is stiffer and stronger,and is used for the radius, frames and anchor threads, which allows the web to withstandprey impact and to keep its structural strength through a wide range of environmentalconditions. 
(A) Two types of silk threads are used in the web. 
(B) The silk threads are made of rare plants in the environment. 
(C) Enclosed in the frame are capture spirals winding round and round from the webcenter out to the frame. 
(D) The main function of the web is to intercept and hold flying prey, such as flies, beesand other insects, long enough for the spider to catch them. 
(E) The orb web is found to have two main characteristics. (F) This type is used in the capture spiral for catching and holding prey.
66