Many kids turn up their noses at the thought of eating fish because, well, it can smell "fishy". While it is usually a healthful source of protein in the diet, there may be several reasons to avoid biting into a forkful of fish. Before you break out the tartare sauce(酸泡菜调味酱), learn some facts about fish to keep yourself and the environment healthy.
Some fish may contain harmful chemicals, which can be the result of both natural causes and water pollution. Mercury(汞) is a toxic chemical, which occurs naturally in oceans and the Earth's crust, but also comes from man-made sources, such as pesticides, burning garbage, and the releasing of fossil fuels.
How do mercury and PCBs end up in fish and the food supply? When they are released into the air, they attach themselves to particles. These particles settle on the ground and in the water and are eventually eaten by microscopic organisms（有机物）.Small fish eat the micro-organisms, and large fish eat the small fish and on up the food chain.
There are also many types of fish that are good for you, but because of overfishing some are in danger of being wiped not. Some are being fished in the wild so much that they cannot reproduce enough to survive. Others are being farmed in ways that are not environmentally friendly.
Despite these problems, there are several fish that are both healthy and sustainable, such as Alaskan salmon, American catfish, Pacific cod, and several farm-raised fish and shellfish.
69. From the first paragraph, we know
B. eating fish can keep yourself healthy.
C. fish is a source of fat in the diet.
D. children hate eating fish because of its smell.
70. PCBs are a group of chemicals that
B. occurs naturally in oceans and the Earth's crust.
C. comes from the releasing of fossil fuels.
D. can be made from burning garbage.
71. Which of the following is the correct order according to the passage?
a. They attach themselves to particles.
b. Small fish eat the micro-organisms
c. These particles settle on the ground.
d. Large fish eat the small fish and on up the food chain.
e. They are released into the air.
f. These particles are eventually eaten by microscopic organisms.
72. What might be the most suitable title for the passage?
A. The way on raising fish.
B. The benefits of eating fish．
C. The kinds of healthy fish.