The selectBox is checked when selectedMountains equals mountain.
当 selectedMountains 等于 mountain 时，selectBox 就是选中的。
youdao
In user interface design, the checkbox group isn't as popular as its cousin, the multi-line selectbox.
在用户界面设计中，复选框组不如它的同类 —— 多行选择框那样流行。
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