write + must do
kaka nakereba naranai
must do; have to do
meaning: must write
宿題、今日じゅうに終わらせなきゃ。
shukudai, kyoujuu ni owarasenakya.
I've gotta finish my homework by the end of today. casual
日本では車は左側を走らなければならない。
nihon de wa kuruma wa hidarigawa o hashira nakereba naranai.
In Japan, cars must drive on the left. neutral