tenses - (verb)ing and (verb)ing with "show"

This is easiest to explain with examples:

Examples

• 1a: Shouting and cursing shows that you are rude.


• 1b: Shouting and cursing show that you are rude.


• 2a: Hitting the target and splitting the arrow shows that he is an
  accomplished archer.


• 2b: Hitting the target and splitting the arrow show that he is an
  accomplished archer.

In cases like this, is "show" or "shows" correct?? If they are both correct, is there any difference in the meaning conveyed? Are there times where one or the other would be more appropriate or effective?