i visited the museums and sat in public gardens 上句中为何museum和

i visited the museums and sat in public gardens 上句中为何museum和garden的后面要加s?还有这个例子America and Americans were prosperous beyond the dreams of the Europeans and Asians whose economies the war had destroyed..其中的european和asian后面也加了s，只是为了形容很多欧洲人和亚洲人吗？