题目内容：
根据以下材料，回答题Japanese Drilling into Core of Earth
In what resembles a journey to the center of the Earth, Japanese scientists have launched the world's first attempt to bore a hole into the red-hot core of a volcano and unlock the secrets of deadly eruption.
A 50-meter-high oil-rig-like derrick perched on the scrubby slopes of Japan's Mount Unzen will begin drilling through the volcano's crust next week in a bid to sample the magma bubbling below.
The aim is to study how the liquefied rock causes menacing gas buildup, said team leader Setsuya Nakata, of the University of Tokyo's Earthquake Research Institute.
"Gassing is important because it controls the explosivity of eruptions," Nakata said. "The results can be expanded to anti-disaster research."
Mount Unzen, a wind-swept 1.486-meter dome on the southern island of Kyushu, is a perfect model. It erupted in 1991, showering avalanches of hot rocks over a nearby town, killing 43 people and leaving nearly 2,300 homeless. Another 11.000 people were evacuated from the area until 1995,when the volcano had stabilized.
The results are particularly important to a nation like Japan, where the meteorological agency monitors 20 dangerous peaks. Perhaps Japan's most famous volcano is snowcapped Mount Fuji,which last erupted in 1707 and sprinkled Tokyo with ash.
The drilling on Mount Unzen will begin very soon from an altitude of 850 meters on its northwest slope. Scientists hope to tap a magma vent around sea level by August and extract a 200-meter-long core sample by summer 2004.
Boring into the glowing magma at that level would normally be impossible, because of its fiery 700 degree Celsius heat. Thus, slurry of water will be pumped into the drill shaft to cool the magma and allow the drill head to cut through.
Nakata said there is no danger of triggering another eruption.
According to the passage, Mount Unzen __________. A．erupted in 1707
B．erupted in 1991
C．erupted in 1995
D．several times in the last century
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