Many people are aware of the beauty of a solar eclipse (日食), but are surprised to learn that lunar eclipses are often just as impressive. While total solar eclipse lasts only for a few minutes and can be seen only in a small area of a few kilometers, total lunar eclipse can last for several hours and can be seen over much of the planet. In fact, the beauty and stability of lunar eclipses make them a favorite of both amateur and professional photographers.
Lunar eclipses generally occur two or three times a year, and are possible only when the Moon is full. When we see the Moon, we are actually seeing sunlight reflected off the surface of the Moon When the Earth is positioned in between the Moon and the Sun, however, the Earth's shadow falls on the Moon, and a lunar eclipse occurs.
The type of lunar eclipse - total, partial, or penumbral (半影) - that occurs depends both on how much of the Moon passes through the Earth's shadow and through which part of the shadow it passes. A penumbral eclipse occurs when the Moon passes through the Earth's outer shadow. This type of eclipse is brief and frequently goes unobserved by all but astronomers. By contrast, total and partial eclipses occur when all or part, respectively, of the Moon passes through the umbra（本影） shadow of the Earth. These eclipses are quite easy to see and are widely observed.
Unlike solar eclipses, lunar eclipses are safe to watch. Solar radiation that occurs during an eclipse of the Sun can cause a form of burns of one's eyes known as eclipse blindness. In fact, the only way to safely view a solar eclipse is by using specially designed equipment. However, since the Moon's light is reflected sunlight, it is completely safe to watch a lunar eclipse without any special equipment, although a pair of binoculars can certainly help the viewer appreciate the beauty of this phenomenon
小题1:The underlined word "stability " most probably means_______.
A．strength
B．position
C．steadiness
D．visibility小题2:According to the passage, a partial lunar eclipse occurs________.
A．when the Moon passes between the Sun and the Earth
B．when all of the Moon passes through the Earth's umbra shadow
C．when only a part of the Moon passes through the Earth's outer shadow
D．when only a part of the Moon passes through the Earth's umbra shadow小题3:The passage implies that penumbral eclipses are________.
A．longer-lasting than most solar eclipses
B．more common than partial or full lunar eclipse
C．the result of the shadow cast by the Moon onto the Earth
D．more difficult to observe than other types of lunar eclipse小题4:According to the passage, it is safe to watch a lunar eclipse, unlike a solar eclipse, because ________.
A．moonlight is less strong than sunlight
B．a lunar eclipse is briefer than a solar eclipse
C．a lunar eclipse lasts much longer than a solar eclipse
D．special equipment can be employed to view a lunar eclipse
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=0，Cu=20kPa；对同样的土进行固结不排水试验，得有效抗剪强度指标：c＇=0，=300°。如果试样在不排水条件下破坏，请回答以下几个问题：