单项选择题：当折现率分别为12%和14%时，某投资项目的净现值分别为16.3万元和-38.8万元

题型：单项选择题

Have you ever rubbed your hands together when they get cold? Why do we do that? We do that for friction. Friction happens when two things that aren’t very smooth (光滑的) rub together to make heat energy. The faster you rub two things together, the more friction you can make. Let’s discover friction!

WHAT YOU’LL NEED:

★Soap ★Water ★Your hands

WHAT TO DO:

★Make sure your hands are dry.

★Rub your hands together until you feel the heat of your hands.

★Now, use soap and water to get your hands very slippery (滑的).

★Try to make friction happen while your hands are slippery.

★Please write down what has happened.

LET’S TALK!

Friction is an energy that happens when two things rub together. When friction happens, it makes heat! When your hands are slippery, they won’t make very much friction and your hands won’t get so hot.

DID YOU KNOW?

★Friction happens when you stop your fast running bike.

★Ancient people made fires by rubbing two pieces of wood together. Friction happened though they didn’t know it. ___ __? Friction is everywhere. Have you ever noticed situations where friction is happening? If not, ask your parents to take you out in a car. If it is not hot, touch the tires (轮胎) of the car before and after a short drive to see how much warmer they get from friction.

小题1:You’d better make your hands ______ to get heat when you rub them.

A. slippery B. dry C. wet

小题2:The word “friction” in the first paragraph means “______”.

A. 摩擦 B. 震动 C. 膨胀

小题3:We can know from the passage that it’s a ______ experiment.

A. physics B. chemistry C. biology

小题4:The topic of the last column (栏目) is ______

A. THINK IT OVER! B. WHAT HAPPENED? C. WORK WITH PARENTS.

小题5:The main idea of the passage is ______.

A. how to discover friction B. how to rub your hands C. how to make fires by rubbing

查看答案

当折现率分别为12%和14%时，某投资项目的净现值分别为16.3万元和-38.8万元

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