赶马女孩子年纪多不过十四五岁，嗓子通常并没经过训练，有的还发哑带沙，____在这种环境气氛里，出口自然，____唱什么，____充满一种淳朴本色美。
He ____ been afraid of dogs ____ ____ since his dad kept a pet dog.
We can't work out the physics problem. Can you tell us________?
先化简，再求值：（1﹣1a-1）÷a2-4a+4a2-1，其中a=﹣2．
