Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

The most important inorganic
substances for living beings are [?],
mineral salts,[?] and
[?]. (There are several
other inorganic substances without
which cells would die.)