云朵cloud既是可数名词，也是不可数名词。
cloud：n.云；云朵；云状物(如尘雾、烟雾、一群飞行的昆虫)；阴影；忧郁
Her father's illness cast a cloud over her wedding day.
她父亲的病给她的结婚喜庆日蒙上了一层阴影。
His last years were clouded by financial worries.
由于经济窘困，他的晚年生活过得闷闷不乐。
He still has a cloud of suspicion hanging over him.
大家仍然在怀疑他。
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