Someone explain that one to me!
有人解释说,一到了我!
Someone must be at the back of this.
这事一定有人在背后捣鬼。
He found someone on him.
他发现有人在跟踪他。
some(something,somebody,someone),any(anything,anybody,anyone),no(nothing,nobody,noone),every(everything,everybody,everyone),all,each,both,much,many,(a)little,(a)few,other(s),another,none,one,either,neither等。