We have progressed a little further with this puzzle, and now arrived at this point. Take a look at
the highlighted '3' and '4'. The '3' clue already has 2 mines next to it. This means that only one
of 'A' or 'E' can be a mine. We don't know which one exactly, but we know that only one of those
will contain a mine.
Now consider the highlighted '4' clue, if one mine is in 'A' or 'E', then we still need another 3
mines for this clue. That means that 'B', 'C' and 'D' must also be mines.
This type of logic and thinking will allow you to solve medium puzzles. To solve hard puzzles you
will need to apply similar types of logic, but looking further forward when trying different
combinations of mines.