“还是” means “or” which indicates 按alternative relation and it’s often used in interrogative sentences.
Subject + （是）+ A + 还是 + B ？
Note that A and B both need to be either noun phrases or verb phrases. A and B can exchange positions and it won’t affect the meaning. As a selective sentence, it can’t apply with “吗”.
这是你的学校还是你的公司？(Zhè shì nǐ de xuéxiào háishì nǐ de gōngsī?) Is this your school or your company?
你想喝水还是喝茶？(Nǐ xiǎng hē shuǐ háishì hē chá?) Do you want to drink water or tea?
现在你是在英国还是美国？(Xiànzài nǐ shì zài Yīngguó háishì Měiguó?) Are you in the UK or the US now?
明天我们坐飞机还是坐火车？(Míngtiān wǒmen zuò fēijī háishì zuò huǒchē?) Shall we take the plane or the train tomorrow?
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