A）realize B）public C）experiment D）pollution E）plastic

The scientist was in a hurry．She had to get some water for her （46） 　　before darkness fell．She was testing the water in the rivers that went into the ocean．Her job was to find out the cause of （47） 　　in the sea at nearby beaches．She lifted out the water and looked angrily at the rubbish in it．Old clothers，（48） 　　bags and pieces of paper were in the dirty water．"Don't people （49） 　　that everything they throw onto the street gets washed into rivers？And they lead right into the ocean!"she said loudly．"How many years will it take to make it clean again？"