Complete the summary of the reading passage by filling each blank with a word or phrase given in the box below.

Gap-fill exercise

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!
   biodiversity      closely connected      discoveries      huge      modern      mysterious      plants and animals      three-quarters   
Though covering (1) of the earth's surface, the ocean has remained (2) to us until recently. With (3) technology we have now made important (4) about the (5) of marine life. We have learnt that whether tiny or (6) , all the (7) of the sea are (8) .