通过切削刃选定点，垂直于主运动方向的平面称为（） A.切削平面 B.进给平面 C.基
题型：单项选择题
问题：
通过切削刃选定点，垂直于主运动方向的平面称为（）
A.切削平面
B.进给平面
C.基面
D.主剖面
题型：单项选择题
Seeing a volcano erupt (喷发) is a wonderful experience, and you can really feel the heat by climbing to the summit of Pacaya for a close-up view. There are guided tours every day up this highly active volcano from Antigua. Giving travelers a chance to see Mother Nature at her most powerful (强大的).
Pacaya is an easy drive from Antigua, a beautiful city with many colorful houses along its old streets that are turned into art-works during its Holy Week festival. No matter when you come to Antigua, you won’t miss the Pacaya-tour companies.
But climbing Pacaya is no easy job: it is 2,560 metres high and reaching the summit takes two to three hours of seemingly one-step-forward and two-step-back movements. As you climb, you hear the sounds of eruptions high above. Smoke, hot remains from recent eruptions begin to line the path as you near the active summit: the McKenney Cone (火山锥). Just as though you were going to walk over to the edge of the cone, the road turns to the left and up to the safety of the old, inactive summit.
Many tours are timed so that you arrive at the cone of the volcano in plenty of time for sunset and the full scene of the erupting red lava (熔岩) in the darkening sky. On a good day the view from the summit is really exciting. The active mouth boils, sending red lava over its sides, and once in a while shoots hot streams up to 100 metres into the air. There is a strong bad smell in the air even if you take care to be upwind of the cone. As evening turns deeper into the night, the burning lava quietly falls down the side of the volcano. For you, too, it is time to get down.
小题1:Many tours are timed for people to _____.
A．get down the mountain in time when night falls
B．avoid the smell from the upwind direction of the cone
C．enjoy the fantastic eruption against the darkening sky
D．appreciate the beauty of the 2,560-metre-high mountain小题2:The word “summit” appears several times in the passage. It means _____.
A．remained, cooled rocks along the path
B．loud sound and terrible smell in the air
C．the most exciting happening in a place
D．the top point of a mountain or hill小题3:What is the main purpose of this passage?
A．To have more tourists come to Pacaya.
B．To describe the beauty of Pacaya.
C．To introduce guided tours to Pacaya.
D．To explain the power of nature at Pacaya.