他们在树苗上罩上一个保护栏。
保护栏位是为了帮助防止外部程式码变更它的值，但可让衍生类别存取。
The field is protected to help prevent outside code from changing its value while allowing derived classes to access it.
他的国籍目前还不知道。他当时是从第2、3排观众的那里跳过保护栏的。
He appeared to have vaulted himself up and over the barricade from the second or third row back.
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