该句话来自于,剑桥英语教材 Unlock3 RW P64 第2段。
There is a wall around the city to keep out the hot desert wind and the streets are narrow ,to provide shade from the sun and allow a breeze to pass through.
后半句话 ",to provide shade from the sun and allow a breeze to pass through."
个人理解是作 the streets are narrow 的目的状语。如果两部分不加逗号直接连接,容易被误解为与are narrow 构成 be adj to do 结构,因此加了逗号以示区分。
个人猜测请高手指正!
There is a wall around the city to keep out the hot desert wind and the streets are narrow, to provide shade from the sun and allow a breeze to pass through.
第二个不定式 to provide...不是表目的,而是表结果。
因为“街道很窄”,所以“可以遮阳”,也可以“让微风穿过”。
用作目的状语的不定式前通常是不用逗号的,但用作结果状语的不定式前面则通常可以用逗号的。