_______ that all mountain roads were closed. A. So the dangerous weather became B. So dangerous did the weather become C. So dangerous became the weather D. The dangerous weather became so
Our environment isn’t as green and beautiful as it should be. There are steel(钢铁) monsters blocking out the sun, blowing out dangerous smoke, and letting out poisonous chemicals into riv
的两条直角边
,
的长分别为
，
，以
交于点
，则
＝ 
.
. 提示:用直角三角形的面积射影定理.