单选题

　　 【填句补文】Mexico's current lack of funds is also partly due to oil. The country has rich oil fields and a few years ago, when oil was expensive, Mexico was selling large quantities of oil to the USA and earning a lot of money. ________. However, the price of oil then dropped, and Mexico has been left owing enormous sums of money and with not enough income from oil sales to pay back the loans.

　　 A、But those ruins are in danger of being seriously damaged by pollution.

　　 B、Scientists estimate that about one millimeter of stone is worn away every twelve years.

　　 C、At others the painted surfaces inside temples are lifting and flaking off and the stone is being eaten away.

　　 D、The government was therefore able to borrow huge sums of money from banks around the world, thinking they would have no problem repaying their debts.