阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。
Prairies are made up of a complete interdepend-ent ecosystem. All kinds of plants and animals in a prairie region depend (1)________one another for survival.
You may think there’s nothing there but grass on a prairie, (2)________ that’s not true. Most of the prairie’s living things are below the ground. Underneath the prairie’s surface are roots and bulbs (根茎) . Some roots of the prairie flowers and grasses run as (3)________ (deep) as 3.5 metres below the ground. It’s important for the roots to run deep because fires are a part of the prairie ecosystem. When a fire (4)________ (burn) through the prairie, plants with shallow (not deep) roots
can not survive. Plants (5)________have deep root systems are able to survive the fire. When fire burns across a prairie, it burns dead plants from the top and returns those nutrients(养料) to the soil. This adds to the (6)_______ (rich) of the prairie soil. This cycle of growth and burning has been going on for (7)________ (thousand) of years.
The American bison (野牛) is the country’s largest land animal. (8)________ (it) home is on the prairies. By1889, Americans had made the bison population to fewer than l, 000 animals. Through great efforts, the bison population has grown to several hundred thousand today.
Humans have put the prairie ecosystem in danger Through constant farming, building, fire prevention, and ignorance (not knowing) of how the prairie works, the United States has (9)________ (lose) much of its natural prairie. Through (10)_______ (educate) and other work, we hope to save some of it.