设是代数系统,+和∘是二元运算.如果满足以下条件:(1) 构成交换群(2) 构成半群(3) ∘运算关于+运算适合分配律则称是一个。
课文理解:Mice and rats are poisoned or trapped, while the gardener wages a never-ending struggle with ragweed, dandelions, slugs and root-rot. We have a modern arsenal of chemical weapons to fight off these invaders and we use them lavishly.Question: What do "chemical weapons" mean in this sentence?
A. guns
B. swords
C. arrows
D. insecticides
Incityapartmentsanddwellings,thepresenceofcockroaches,fleas,ants,mosquitoesorhousefliesisguaranteedtoelicitthesprayingofinsecticides.Miceandratsarepoisonedortrapped,whilethegardenerwagesanever-endingstrugglewithragweed,dandelions,slugsandroot-rot.Wehaveamodernarsenalofchemicalweaponstofightofftheseinvadersandweusethemlavishly.Question:Which of the following is such an "invader"?
A. gardeners
B. insecticides
C. slugs
D. dwellings
The urban message kids get runs completely counter to what they are born with, a natural interest in other life forms.Question: For "urban message " , it could refer to the following answers except ___________.
A. Human beings are a part of nature.
B. Nature is dirty.
C. Nature is dangerous
D. Nature is our enemy.