那突如其来的电闪雷鸣预示着一场严重的暴风雨即将来临。

The sudden lightning and thunder were ___portentous signs of a severe storm approaching.

他那故作庄严的讲话方式让整个房间的气氛变得很尴尬。

His ___portentous manner of speaking made the whole room feel awkward.