volunteer uses a truck to pick up donations of unsold food and clothing from　stores and to deliver them to locations where they can be distributed. He　drives only along a certain network of roads.　

 
　　In the network there are two-way roads connecting each of the following pairs　of points: 1 with 2, 1 with 3, 1 with 5, 2 with 6, 3 with 7, 5 with 6, and 6 with 7.　There are also one-way roads going from 2 to 4, from 3 to 2, and from 4 to 3. There　are no other roads in the network, and the roads in the network do not intersect.　

　　To make a trip involving pick-ups and deliveries, the volunteer always takes a　route that for the whole trip passes through the fewest of the points 1 through　7, counting a point twice if the volunteer passes through it twice.　

　　The volunteers home is at point 3. Donations can be picked up at a　supermarket at point 1, a clothing store at point 5, and a bakery at point 4.　Deliveries can be made as needed to a tutoring center at point 2, a distribution　center at point 6, and a shelter at point 7.　If the volunteer starts at the supermarket and next is to go to the shelter,　the first intermediate point his route passes through must be

　　2

　　3

　　5

　　6

　　7

　　答案：(B)

　　If starting from home, the volunteer next is to make pickups for the shelter　at the supermarket and the bakery (in either order), the first two intermediate　points on his route, beginning with the first, must be

　　1 and 2

　　1 and 3

　　2 and 1

　　2 and 4

　　4 and 2

　　答案：(A)

　　If starting from the clothing store, the volunteer next is to pick up bread at either　the supermarket or the bakery (whichever stop makes his route go through the　fewest of the points) and then is to go to the shelter, the first two points he　reaches after the clothing store, beginning with the first, must be

　　1 and 2

　　1 and 3

　　4 and 2

　　6 and 2

　　6 and 4

　　答案：(B)

　　If the volunteer is to make a trip starting at the shelter, next going to the　bakery for a pickup, and then ending at the distribution center, the first two　intermediate points on his route, beginning with the first, can be

　　3 and 1

　　3 and 4

　　4 and 2

　　6 and 2

　　6 and 5

　　答案：(D)

　　A developer is planning to build a housing complex on an empty tract of land.Exactly seven different styles of houses-Q, R, S, T, W, X, and Z-will be built　in the complex. The complex will contain several blocks, and the developer　plans to put houses of at least three different styles on each block. The　developer will build the complex according to the following rules.　

　　Any block that has style Z on it must also have style W on it.

　　Any block adjacent to one that has on it both style S and style X must have on　it style T and style Z.

　　No block adjacent to one that has on it both style R and style Z can have on　it either style T or style W.

　　No block can have on it both style S and style Q.

　　Which of the following can be the complete selection of house styles on a　block¡

　　Q, R, S

　　Q, S, X

　　R, T, Z

　　S, W, Z

　　T, X, Z

　　答案：(D)

　　读题：一个房地产开发商计划在一块空地上建造housing complex。共有7种不同风格的房屋Q、R、S、T、W、X、Z, The Complex包含几个街区，每个街区至少包含3种不同风格。

　　写条件：

　　　1、 Z → W (表示有Z就必有W)

　　　2、（S，X）→ （T，Z）相邻 (表示与具有（S，X）风格街区相邻的街区必须有T，Z)