纺织厂里有一道工序叫“梳棉”，只有将杂乱无章的棉絮梳理成顺直的棉絮条后，才用于纺线. 梳棉车必须保持一定的潮湿程度，以防止因为_____而造成的不便和危害.

The students are going to raise some money           the poor            the afternoon of May 21st.

A．to; on

B．for; on

C．to; in

D．for; in