一旦他拿定主意，有时会相当固执。

He ___can be quite stubborn when he's made up his mind.

周末的公共交通有时不太靠谱。

Public transportation ___can be unreliable on weekends.

这里的夏季天气有时会非常难以预测。

Summer weather here ___can be very unpredictable.