Honeybees are disappearing for unknown reasons around the Un

Honeybees are disappearing for unknown reasons around the United States. Last winter, bees disappeared from 23 percent of American beekeeping businesses. Causes of the phenomenon, however, have remained a mystery.
Now, scientists from several universities and the United States Department of Agriculture say they have a possible explanation for the bee decline（数量下降）. It is a little known virus called Israeli acute--paralysis virus (IAPV) .The virus kills bees. Researchers in Israel first described it in 2004 , but until now, bee experts hadn’t paid much attention to it.
When trying to find out why the bees were disappearing, a research team at Columbia University studied bee colonies ( 群体), some with and the others without decline. The research turned up large numbers of two types of fungi (真菌) once suspected of causing the bee decline. The research results, however, showed that the fungi were almost as common in colonies without a decline as they were in colonies with a decline. The researchers concluded that the two fungi probably weren’t the cause.
Studies of the presence of IAPV, however, showed more interesting information. In those studies, done by a team at Pennsylvania State University in University Park, the virus showed up in 83 percent of samples from colonies with symptoms (症状). Only five percent of samples from symptomless colonies had it.
Scientists still don’t know whether IAPIV can single--handedly cause the bee decline. They believe that even if the virus is making colonies sick , it could have a partner in crime. It’s possible, for instance, that insects or chemicals in the environment weaken bees, making them more likely to catch IAPV.
Scientists are still trying to figure out how IAPV came to the United States. The United States currently allows bee products to be imported from Canada, Australia, and New Zealand. If it turns out that this trade is spreading disease, the rules might eventually change.
68. According to the passage ，IAPV is a virus that ______.
A. hasn’t attracted much attention
B. well-known to doctors and scientist
C. was first found by Austrian researchers
D. is dangerous to animals and human beings
69. The underlined sentence in the fifth paragraph probably means______.
A. the virus could also cause other damages
B. there must be something that is the real cause
C. IAPV is not the only cause for the bee decline
D. the virus may be caused by the polluted environment
70. From the third and fourth paragraphs, we know researchers draw their conclusions by means of _______.
A. calculating B. comparing C. examining D. investigating
71. What still remains unknown to American scientists according to the passage?
A. How and why to kill IAPV.
B. How IAPV came to America.
C. Whether bee products should be imported.
D. How to change the rules of the bee products trade.
72. The best title for this passage would be _____.
A. Bee Disease B. How to Kill IAPV
C. A Virus—IAPV D. Two Types of Fungi