题目

阅读短文，根据短文内容回答问题。 Chris is not a traditional explorer（探险者）— he usually works in an office for a large organization. Yet his job can sometimes be just as exciting and dangerous as being an explorer. Chris works for MSF, an organization also known as Doctors Without Borders (无国界医生). MSF sends trained doctors all over the world to help people after a war or a disaster. Chris is a doctor from France who has travelled to many places to organize programmes that help people. At the moment, there are over 27,000 trained doctors and nurses ta4．下列选项中，全部属于大量元素的是（　　）A．P、N、Mn、KB．N、S、Cu、PC．Fe、S、P、ND．Ca、N、P、K