Optional argument
[计] 任选变元
🧩 词语组成解析
🗣️ 情景例句
Sure. It's up ahead to your left.
好的。往前走，在你的左边。
May I have this?
我能拿这个吗？
We tramped through the wood for over two hours until we arrived at a deep stream.
我们在树林中跋涉了两个多小时，到了一条深溪边。