immune system

一种化学物质，通常有酸味，有时能燃烧或溶解东西。在科学上，它是pH值小于7的液体。

代数是数学的一个分支，使用字母和符号来代表数字。它用于通过遵循特定的数学规则来寻找未知值。

An atom is the smallest possible part of a chemical element. Everything in the world is made of millions of these very tiny particles.

Atomic relates to the very small parts called atoms that make up everything in the world. It is often used to describe science, energy, or very small things.

Calculus is a high-level branch of mathematics that studies how things change. It uses special symbols to calculate things like the speed of an object or the area of a shape.

A catalyst is something that makes a change happen faster or more easily. In science, it is a substance that speeds up a chemical reaction without being changed itself.

电路是电流流过的完整路径。它就像一个封闭的圆圈。

The circumference is the distance around the outside edge of a circle or a round object. It is a measurement that tells you how long the boundary of a round shape is.

常量是指保持不变的事物。在数学中，它是一个固定值。

A decimal is a number that uses a dot to show parts of a whole. It is based on the number ten and helps show values smaller than one.