The construction company has a clause in its contract
which requires it to complete the building project in nine months.
~~~~~
上句這一句出自一本書的例句，應是無誤。
但為什麼文法檢查工具，一直建議我 把 which 換成 that。
換成that之後，又說整句不Clarity.
向高手請益，謝謝。