A、Zika. B、Mosquitoes. C、Malnutrition. D、Unknown yet. D录音提到，世界卫生组织(WHO)的一份报告明确指出巴西microcephaly爆发的成因还没确定(yet to be determined)，故D项

Health officials in Brazil have declared a state of emergency in several states. They are also warning women not to get pregnant. These extreme actions are the result of a recent rise in birth defects. About 2,400 babies in Brazil were born recently with extremely small heads. The babies have a condition called microcephaly. Microcephaly causes severe brain damage. To date, 29 of these babies have died. The number of microcephaly cases in Brazil is about 10 times higher than what the country usually sees in a year. The U.S. Centers for Disease Control (CDC) explains on its website that there are many causes of microcephaly. And the World Health Organization (WHO’) said in a statement that the cause of the microcephaly outbreak in Brazil had yet to be determined. However, the CDC says the link between a virus infection and microcephaly is being investigated. The virus is called Zika.
    Zika is spread by mosquitoes. Some babies in Brazil with microcephaly have tested positive for the Zika virus while others have tested negative. The CDC says that Brazil reported its first case of Zika virus in May. Since then, the virus has spread and has caused infections in many Brazilian states and other countries in Latin America According to other news agencies, health officials have reported many cases of microcephaly in Rio de Janeiro and Sao Paulo. Reuters news agency reports that the Zika virus has been confirmed this year in Panama, Venezuela, El Salvador, Mexico, Suriname, Colombia, Guatemala and Paraguay. Zika is also found in Africa and Southeast Asia. The CDC has a webpage with information on Zika. It says that because the "mosquitoes that spread Zika virus are found throughout the world, it is likely that outbreaks will spread to new countries." The CDC says the common symptoms of Zika are fever, rash, headache, joint pain and red eyes. Zika causes mostly mild symptoms in adults. However, in newborns the disease can cause severe brain damage. There is no medicine to treat Zika. Travelers and especially pregnant women are advised to protect themselves by avoiding mosquito bites. Health officials around the world are watching the situation closely.
23. Why do the officials warn women not to get pregnant?
24. What is the cause of microcephaly’s outbreak in Brazil?
25. What can travellers do to protect themselves from Zika?