In this example, the nouns, person, tree, wall, cat and bird, all take the indefinite article but only when they're first introduced.

在这个例子中，名词，人，树，墙，猫和鸟，所有都加不定冠词，但这是只在他们被第一次介绍时。

Time of day. Brightness of the sun. Shadows from trees, walls and buildings. These all influence how much sunlight falls, or does not fall, on plants.

一天中的时间。 太阳的亮度。 来自树木、墙壁和建筑物的阴影。 这些都会影响阳光落在或没有落在植物上的程度。