问题
选择题
下列方程中，是一元一次方程的是（ ）
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答案
A、未知数的最高次数是2，它属于一元二次方程．故本选项错误；
B、由原方程得到y+2=0，符合一元一次方程的定义．故本选项正确；
C、该方程中含有两个未知数，属于二元一次方程．故本选项错误；
D、该方程属于分式方程．故本选项错误．
故选B．
搜题请搜索小程序“爱下问搜题”
下列方程中，是一元一次方程的是（ ）
|
A、未知数的最高次数是2，它属于一元二次方程．故本选项错误；
B、由原方程得到y+2=0，符合一元一次方程的定义．故本选项正确；
C、该方程中含有两个未知数，属于二元一次方程．故本选项错误；
D、该方程属于分式方程．故本选项错误．
故选B．
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| We have always been warned of the dangers of forest fires. They cause 1 to a forest. They kill many plants and animals in an eco-system, which is a group of living things and their environment. But have you ever heard of a forest fire that can be 2 for a forest? People start some of the fires with a special reason to actually do good to the eco-system. In fact, fires are a natural part of any eco-system. Without fires, the oldest and largest trees would stop sunlight from reaching the forest floor. Fires can 3 some of these old trees. When the trees die, they provide something good for the earth. New trees can grow strong and healthy in their place. Some trees even need fires to grow. These trees hold their seeds (种子) inside. Heat from a fire allows the coat of the seeds to open up. Then the seeds fall to the ground and have the 4 to grow/ Scientist, who know about nature's needs, start some of these fires, called controlled burns. A fire is started and kept under control. This way, the fire does not spread out of the area or 5 a after forest fires, they can go hungry 6 their food has been damaged in the fire. Small, controlled fires mean than animals will not have to move far to find food. After some time, small plants begin to grow. Animals return soon after the plants return. This 7 makes an eco-system. So the next time you hear about a forest fire, think about the good as well as the bad. It may take a new eco-system a while to return, but it will likely come back stronger and healthier than ever. | ||||
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