In variable practice, your brain is more actively engaged and actively processing information, which allows it to hold information better.
在变化练习中，大脑更积极参与，积极处理信息，这使大脑更好地保持信息。
There is one change of variable problem on each of the two practice exams to give you a feeling for what's realistic.
两次练习测验中,都有一道题是关于变量替换的,感觉这是很重要的那样。
Always initialize your variables. PHP will automatically create a variable if it hasn't been initialized, but it's not good practice to rely on this feature.
当需要没有初始化的变量，PHP解释器会自动创建一个变量，但依靠这个特性来编程并不是一个好主意。
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