In spite of the heavy rain, she went to the shop. 尽管雨很大，她还是去商店了。From the look of the sky we shall have heavy rain this afternoon. 从天空的模样来判断，今天下午会下大雨。第二个句子我认为是错的，应该改成：From the look of the sky we shall have a heavy rain this afternoon. 因为在表示自然现象的名词前，可以使用定冠词the，例如：the rain 雨，the wind风, the fog雾， the snow雪, the air空气, the storm风暴， the snowstorm 暴风雪，等。例如：The fog was so thick that we couldn't see the top of the hill. 雾很大，我们看不见山顶。The wind blew down the trees. 风把树刮倒了。The rain has cleaned the air.下雨净洁了空气。Don't stand in the rain. 不要站在雨中。The ship sank in the storm. 船在风暴中沉没了。 但是要注意的是：当这类名词前有形容词修饰时，可用不定冠词，表示“一场，一阵，一种”等含义。这也是我说您第二个句子错误的原因。再例：A cold wind is blowing from the north. 冷风从北方吹来。There was a heavy rain last night. 昨晚下了一场大雨。A heavy snow is falling outside. 外面正下着大雪。 另外，当这类名词表示一般物质时，不用冠词。例如：Rain falls in summer; snow falls in winter. 夏天下雨，冬天下雪。Man can't live without air. 没有空气人不能活。