Countries, US States, Capitals, Elements, 100 Most Common Words: add 3 letters to get another

Add 3 letters to the ones of the answer on the left and you'll get the letters of the answer on the right!
Hints: in each answer you are shown in capital letters the letter that starts the answer next to it and in small letters the one that ends it.
Example: from the hints in the first pair you can understand that the 'from' word starts with C and the 'to' word start with a letter that isn't present in the 'from' word