2. The following procedures are available: 1. a:= 1； 2.b:= a； 3.d:=-a； 4.e:= a+d； 5.c:= 2 * d； 6.f:= b+ e-d； 7.g:= a * f+c； Now it is necessary to distribute this program to several (enough) pc computers connected by cables for parallel execution. Each PC executes some of these statements, and can communicate with other PCs through cables at any time to exchange some intermediate results. Suppose that each PC can execute one sentence per unit time, not counting the time spent on communication. This program can be completed in unit time at the earliest. Note: Any intermediate result can only be quoted by other computers after it is obtained on one computer. For example, if statements 4 and 6 are distributed to two PCs for execution, statement 6 must be executed after statement 4 because it needs to refer to the calculation result of statement 4. (noip2009 preliminary examination questions) 2. There are three extracurricular groups: physics group, chemistry group and biology group. Today, there are five students, Zhang, Wang, Li, Zhao and Chen, who are well known.

Zhang and Wang are members of physics group, Zhang, Li and Zhao are members of chemistry group, and Li, Zhao and Chen are members of biology group. If you want to join

Three groups choose three team leaders, and one classmate can only be the team leader at most. * * * has seeds.

Select the scheme. A furniture company produces tables and chairs. There are now 1 13 units of wood. Each table should use 20 units of wood at the price of 30 yuan; Wood per chair 16 unit, 20 yuan. Using the existing wood to produce tables and chairs (without using all the wood) can sell for up to RMB. 75 children went to the playground to play. They can take a merry-go-round, a sliding railway and a spaceship. It is known that 20 of them have played these three things, and 55 have played at least two of them. If the cost of each ride is 5 yuan, and the total income of the amusement park is 700, you know that no child has ever played. (preliminary test of noip2004) 1. There are four different books a, b, c and d on the shelf. Where a and b are red and c and d are black. There are _ _ _ ways to put these four books on the shelf so that all the black books can be arranged together. In order to meet the requirement that A must be to the left of C, all books with red covers should be put together, and all books with black covers should be put together. * * * There are _ _ _ kinds of arrangements. These questions are not very difficult.