用乘法分配律，结合律、交换律计算以下各题：
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（1）25×19×4，
=19×（25×4），
=19×100，
=1900；
（2）（25×125）×（8×40），
=（25×40）×（125×8），
=1000×1000，
=1000000；
（3）35×39+65×39，
=（35+65）×39，
=100×39，
=3900；
（4）36×199+36，
=36×（199+1），
=36×200，
=7200．
Reduce means “use less”. Don’t waste things. This ___小题3:__money and reduces pollution and waste going into the environment. Before we buy something new, think __小题4:___it is really necessary—or maybe the old one will be just as good! When we do buy things, choose local products if __小题5:____ and try not to buy too many things from abroad. Reuse means “use again”. Use things for as long as possible. When we buy things, make sure that they __小题6:_ a long time. We should look after them__小题7:__ they will last and we should repair them if we can instead of throwing them away and buying new ones. Don’t use a paper cup or a paper bag. It’s better to use a china cup and a lunch box because you can use them __小题8:_. Recycle means “change things into something else”. Although it takes __小题9:__ to change something into something else, it’s better than throwing things away or burning them. Find out what can be recycled in your_小题10:___ and take part in recycling programmes. We should also buy products made from recycled materials, such as recycled paper, to help save trees. |