Differences between: 过来, 起来, 下来 I encountered this multiple choice question:

这件事情说__________简单，做__________难

Where among the choices there are: 过来，起来，下来。
I always thought that their meaning was the same, but in this case the right answer is 起来.
So what's the difference between them? What do they actually emphasize in this specific case and in more general sentences?
过来 means "come over/ come here", 坐过来 means "sit over here"

下来 means "come down/ get down here) 坐下来 means "sit down"

起来 if used by itself, means "get up/ stand up", also carries a sense of "direction." when used in a combo like 
说起来 (when being talked about) 做起来 (when being worked on) it carries a meaning of "being brought up" or "being initiated." In this case, its usage is not necessarily indicative of "direction."

all three can be used by themselves or in a combo like the examples i give.