怎么 zěn me is used in rhetorical questions to convey a more contentious enquiry before a verb or modal verb:
他怎么会不明白呢？
Tā zěn me huì bú míng bái ne ？
How (on earth) can/could he fail to understand?
你怎么能不去呢？
Nǐ zěn me néng bú qù ne ？
How can you not go?
你怎么可以怪她呢！
Nǐ zěn me kě yǐ guài tā ne ！
How can/could you blame her! (implies ‘You can’t blame her.’)
你怎么可以这么说呢？
Nǐ zěn me kě yǐ zhè me shuō ne ？
How can you put it like that?/How can you say that?
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.
