Read the following passage, and mark the letter A, B, C, or D on your answer sheet to indicate the correct word for each of the blanks from 19 to 28. Any change in one part of an ecosystem can cause changes in other parts. Droughts, storms and fires can change ecosystems. Some changes ___19___ ecosystems. If there is too ___20___ rainfall, plants will not have enough water to live. If a kind of plant dies off, the animals that ___21___ it may also die or move away. ...

Read the following passage, and mark the letter A, B, C, or D on your answer sheet to indicate the correct word for each of the blanks from 19 to 28.

Any change in one part of an ecosystem can cause changes in other parts. Droughts, storms and fires can change ecosystems. Some changes ___19___ ecosystems. If there is too ___20___ rainfall, plants will not have enough water to live. If a kind of plant dies off, the animals that ___21___ it may also die or move away. Some changes are good for ecosystems. Some pine forests need ___22___ for the pine trees to reproduce. The seeds are sealed inside pinecones. Heat from a forest fire melts the seal and lets the seeds___23___. Polluting the air, soil, and water can harm ecosystems. Building ___24___ on rivers for electric power and irr igation can harm ecosystems ___25___ the rivers. Bulldozing wetlands and cutting down ___26___ destroy ecosystems. Ecologists are working with companies and governments to find better ways of ___27___ fish, cutting down trees, and building dams. T hey are looking for ways to get food, lumber, and other products for people ___28___ causing harm to ecosystems.

Điền vào số 21