一个 史上很难 的英语句子的解释---------不是高手勿进

一个 史上很难 的英语句子的解释---------不是高手勿进
Fireworks were lit long before the moon came out.The big noise brought people out into the warm night to enjoy the interesting scene.Everywhere,there were the paper remains of used fireworks lying on the ground.Little boys lit more and covered their ears as they waited excitedly for the explosions.
The moon appeared above the horizon（地平线）：huge,silver ball high above the city,and the streets filled with people,as Java began to enjoy one of the year’s greatest events：‘the Night of the Full Moon’,a festival that is especially popular with young people.
More and more young Javanese gathered together and walked slowly through the night.Joking and chatting,they moved towards the mountain on the edge of the city.They continued to climb until they reached the old temple at the top of the mountain.
After they were inside the temple,they drank their water and ate their moon-cakes-delicious homemade ones,full of dried fruit and nuts.Outside,on the mountain,young people sat cross-legged in circles,chatting and telling each other jokes.【And still,in their hundreds,more young people continued to make their way up the mountain to admire the brightly shining moon.】
重点解释in their hundreds中的hundreds是名词吗?in是在---里吧?
我翻译起来总觉得别扭,”在他们的百里“.郁闷了
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in their hundreds,成百上千的.
再问： in their hundreds 做什么句子成分，修饰谁？
再答： 作状语，修饰more young people.