write + because
kaku kara
because; so — the speaker's own reason
明日テストがあるから、今夜は遊べないよ。
ashita tesuto ga aru kara, kon'ya wa asobenai yo.
I've got a test tomorrow, so I can't hang out tonight. casual
先に帰るね。明日も早いから。
saki ni kaeru ne. ashita mo hayai kara.
I'm heading home first — I've got another early start tomorrow. casual