参考答案：D

解析：结构识别。be about to occur将要发生；imminent即将来临的，逼近的：He was faced with imminent death．他面临逼近的死亡。adjacent邻近的：adjacent cities相邻的城市。gigantic巨大的；庞大的：The new airplane looked like a gigantic bird．这架新飞机看起来像一只巨大的鸟。perilous危险的：a perilous．journey across the mountains横越重山的艰险征途。