That last one was the best.
I had difficulty understanding the dialogue in most of these. If English isn't your native language, consider writing in your native language.
Even when I did understand, I often didn't find them humorous. Remember, just because something would be funny if it happened in real life doesn't mean that it will be funny in a comic. Look at other comics (or comedians, movies, whatever) that you find funny, and think about what makes them work. Pay attention to the elements of a joke -- the set-up and the punchline. Your last comic is funny because something is happening that isn't what we'd expect. Try to work with that: use the first two panels to make us expect something, then, in the last panel, deliver a punchline that shatters that expectation. Here's a great example:
/comics/allenhenderson/5224/
Keep working on it. Good luck. Welcome to stripcreator.