定积分 $\int \begin{array}{c}1\\ 0\end{array}\left(\sqrt{1-{\left(x-1\right)}^2}-x\right)dx$ 等于（   ）

    In our town, there is a big zoo with a lot of animals in it. There are so beautiful tigers and two old lions. They eat a lot of meat every day.
There are also two big elephants and one baby elephant. The elephants are kind animals. They eat a lot every day. They like children. Children often give them bread and bananas. Elephants like bananas best.
    In our zoo there are also brown bears, black bears and white bears. They stand on their hind legs, hold up their four legs and ask for food. They like cakes very much.
    There's also a children's corner in our zoo. Children ride horses and donkeys and watch the monkeys there. The monkeys are very funny. They climb up ropes and jump down again and play with each other like small children.

市场上有“加碘食盐”、“加铁酱油”等商品，这里的“碘、铁”应理解为（  ）