Nicaragua's  Cerro Negro Volcano has erupted 23 times in the past 100 years,burying homes, crops and people in lava and ashes. But recently the black mountain has become a tourist draw, thanks to a newly invented extreme sport: volcano boarding. Thousands of thrill-seekers have climbed to the top of Cerro Negro, peered into its mouth, then zipped down its rough-and--rocky 41--degree slope on special boards. The volcano-boarding speed, set by an Israeli woman, is 54 mph. "Rushing down an active volcano is something that people expect." Said Anthony   Alcalde, an expert volcano boarder. The sport was developed in the mid-2000s by Darryn Webb, an Australian who had climbed the nearby Cerro Negro but was looking for a faster way to get to the bottom. He tried sliding down on surfboards, snowboards, and even a refrgerrator door before inventing a sit-down board made of plywood. "At first, Darryn planned to use a snowboard," said Gemma Cope, a British woman who now runs Big Foot, which offers volcano boarding tours. "But he realized he couldn't cut an edge for there were little rocks everywhere. So he came up with the sitting-down option and realized he can go pretty fast. "  Tourists,who are nearly all foreigners,pay $28 for the experience, which begins with a truck ride on dirt roads to Cerro Negr0.a 2,400-foot--high volcano that last erupted in l999.Visitors must carry their boards during the half-hour climb to the top. There,they go straight down the slope and sometimes they have to use their feet for brakes.Along the way.The board fills with rocks and dust,making boarders almost blind.Crashes are common."l wiped out twice and ripped my pants."said Melinda Vorisek, a tourist from Miami."But I'd do it again." Another tourist added:"It was sheer terror. I was eating dirt.But how many people can say they've bombed down a volcano?" what adds to the danger of volcano boarding according to the passge?
The rocks and dust raised by boards. The sudden eruption of the volcano. The lack of professional equipment. The rough and steep slope of the hill.
Question: Nicaragua's  Cerro Negro Volcano has erupted 23 times in the past 100 years,burying homes, crops and people in lava and ashes. But recently the black mountain has become a tourist draw, thanks to a newly invented extreme sport: volcano boarding. Thousands of thrill-seekers have climbed to the top of Cerro Negro, peered into its mouth, then zipped down its rough-and--rocky 41--degree slope on special boards. The volcano-boarding speed, set by an Israeli woman, is 54 mph. "Rushing down an active volcano is something that people expect." Said Anthony   Alcalde, an expert volcano boarder. The sport was developed in the mid-2000s by Darryn Webb, an Australian who had climbed the nearby Cerro Negro but was looking for a faster way to get to the bottom. He tried sliding down on surfboards, snowboards, and even a refrgerrator door before inventing a sit-down board made of plywood. "At first, Darryn planned to use a snowboard," said Gemma Cope, a British woman who now runs Big Foot, which offers volcano boarding tours. "But he realized he couldn't cut an edge for there were little rocks everywhere. So he came up with the sitting-down option and realized he can go pretty fast. "  Tourists,who are nearly all foreigners,pay $28 for the experience, which begins with a truck ride on dirt roads to Cerro Negr0.a 2,400-foot--high volcano that last erupted in l999.Visitors must carry their boards during the half-hour climb to the top. There,they go straight down the slope and sometimes they have to use their feet for brakes.Along the way.The board fills with rocks and dust,making boarders almost blind.Crashes are common."l wiped out twice and ripped my pants."said Melinda Vorisek, a tourist from Miami."But I'd do it again." Another tourist added:"It was sheer terror. I was eating dirt.But how many people can say they've bombed down a volcano?" what adds to the danger of volcano boarding according to the passge?
A. The rocks and dust raised by boards.
B. The sudden eruption of the volcano.
C. The lack of professional equipment.
D. The rough and steep slope of the hill.
Answer: