Imagine fishermen walking down to the seashore, ready to carry out their early morning routine of preparing their boats and net.(1) _____ they hope for a good catch of fish.But to their (2) _____, a horrible sight meets their still sleepy eyes.Thousands of-fish have been washed ashore dead.The cause of this mass destruction is red tide!

　　Red tides are a global (3) _____.They have been observed on both the Atlantic and the Pacific coasts of the United States and Canada.They have also occurred in many other places.Though relatively few people are (4) _____ them, red tides are not new.

　　In the Philippines, a red tide was first seen in the province of Bata an in 1908.Since then, red tides have been seen in many other (5) _____ A Philippines red tide expert told us that “(6) _____ the fish kills, the Philippines has documented 1926 eases of dead shellfish poisoning caused by red tides.”

　　The term “red tide” (7) _____ the discoloration of water that sometimes occurs in certain areas of the ocean or sea.Although the color is often red, it may also be (8) _____ of brown or yellow.The World Book Encyclopedia reports that “the discolored areas may range from (9) _____ a few square yards to more than 2600 square kilometers.”

　　What causes such discoloration? Red tides are generally caused by several species of single-celled organisms.These tiny organisms have hair-like projections which they use to (10) _____ themselves in water.There are about 2000 varieties of these organisms, 30 of which carry poisonous substances these minute organisms usually stay in warm waters with high content of salt.
____

A.assured of

B.worried about

C.concerned about

D.aware of