Misc: Year in which Margaret Thatcher became PM?

Questions

What do the letters 'r.e.m.' stand for?

What do the words 'par avion' on the outside of an envelope mean?

What do we call the noise made by a sudden spasm closing the windpipe?

What do x & y chromozomes combine in making ?

What do you call a creature that is going to change into a frog?