居民楼内堆放杂物有哪些危险性？
参考答案：
（1）易引起火灾，并使火灾扩大蔓延（2）发生火灾后，通道堵塞，人员、物资不易疏散（3）妨碍火灾的扑救
Europe has achieved more in controlling the AIDS virus than Asia in the past ten years, ________ the number of people infected with the virus is going up sharply.
A．when
B．that
C．so that
D．where
根据下面的电路原理图，该转换器是（）。
A、降压
B、升压
C、降压-升压
D、线性稳压器
