定语从句中,从句的关系代词与先行词相同,并且从句动作是由先行词发出的,省略关系代词和be动词,并将从句中的谓语动词做相关变化,主动态的变为进行时,被动态的变为过去分词.
本句的含义是：艺术展馆前有数百人在等候欣赏梵高的画作.
主动态的用v-ing.形式；v-ed指的是被动的.在这里作定语.
如：
there is a man
a man is sitting in the armchair.
——there is a man sitting in the armchair
there is a man who is sitting in the armchair.
here is a building which is built in the year of 2009
-----here is a building built in the year of 2009
i saw a man who was smoking by the gate
-----i saw a man smoking by the gate
i got that book which is written by a famous writer
----- i got that book written by a famous writer
这种省略很常见,建议多留意,多积累!