很高兴能够在这里回答你的问题：
Doctor John is walking to his hospital.改为
Doctor John is(going on foot )to his hospital.
这里walk to意思是步行去,不是散步,所以不用take a walk,而用go on foot
It is possible for fire to cause danger if we are not careful改为
Fire( may be)danger if we are careless.
Mrs Sun couldn't get out because she hurt her leg改为
Mrs Sun(wasn't able to )get out because she hurt her leg.
或
Mrs Sun(was unable to )get out because she hurt her leg.