L4
讲座
1. What is the main purpose of the lecture?
To examine a new theory about the origin of comets
To illustrate the difficulty of studying comets near the Sun
To explain ways in which comets are affected by the Sun
To discuss the forces that influence a comet’s orbit
2. According to the professor,what produces a comet’s coma?
Particles attracted to the comet as it moves through space
Vaporization of frozen gases in the comet’s nucleus
Variations in the speed of solar winds
Irregularities in the crust covering the comet’s nucleus
3. According to the professor,what made it impossible for astronomers to directly observe a comet’s nucleus until recently?（多选题）
The brightness of the comet’s coma
The unpredictability of the comet’s orbit
Interference from solar radiation
The size of the nucleus
4. Why does the professor discuss solar radiation and solar winds?
To show how the crust of a comet’s nucleus is formed
To suggest possible causes for the unpredictability of a comet’s speed
To explain the difference between two types of comet tails
To provide an example of forces whose effects on comets are not well understood
5. Why does the professor mention an airplane’s exhaust?
To help students imagine the length of a comet’s tails
To describe the interaction of materials in a comet’s tails
To indicate the types of gases that are present in a comet’s tails
To help explain his point about the direction of a comet’s tails
6. Why does the woman say this:
To express confusion about something the professor just said
To confirm that she understands the professor’s explanation
To propose a different explanation from the one the professor gives
To respond to the professor’s request for information
