Because

因

yīn

(by or for the cause that; on this account that; for the reason that)

因為 /因为

yīnwèi

(by or for the cause that; on this account that; for the reason that)

由於 /由于

yóuyú

(by or for the cause that; on this account that; for the reason that)

沒有為什麼 /没有为什么

méiyǒu wéishénme

(word used in place of an answer to "why")

沒為什麼 /没为什么

méi wéishénme

(word used in place of an answer to "why")