题目内容：

It was a physical class. But it was nothing like previous ones — the class was “attended”

by over 60 million students across China, and the teacher was not even on the planet: she was 340 kilometers above the earth.

“Hello, everyone. I’m Wang Yaping. I’ll host your lecture today.” Smiling to the camera, Wang, China’s second female astronaut, started her video class on June 20 on board the Tiangong-1 space station.

To show how Newton’s Laws work in space, Wang and her fellow astronauts used simple items like balls and spinning tops. The highlight of the lecture was when Wang made a film of water using a metal ring, something that only happens in zero gravity, where the surface tension(张力) of water is much higher than it is on the earth. She then took it a step further by pouring more water onto the film and turning it into a water ball, leaving the audience amazed by what they saw.

The 40-minute lesson seemed to have passed too quickly for students to see enough of those magical experiments. But sending stuff into space is really expensive. According to The Beijing Times, every kilogram launched into space cost 20,000 dollars. The experimental items taken this time were all strictly selected and weighed about 2.9 kilograms in total. This adds up to quite a large price tag.

The organizers of the event also had to consider the time of day: the communication signal between the earth and Tiangong-1 was best during that specific 40 minutes, when the spacecraft was flying within the coverage of all of the ground-based testing stations.

1.Why is the class different from a common one?

A. Because it took 40 minutes.

B. Because over 60 million students across the world attended it.

C. Because the teacher was on the planet.

D. Because the lecturer was in space.

2.One of the experiments shows         .

A. object motion under weight conditions

B. laws of physics under weightless conditions

C. laws of physics under weight conditions

D. how Newton’s Laws work on the earth

3.Which phrase can best replace the underlined words in the passage?

A. took a photo of water.

B. recorded moving pictures of water.

C. made a thin layer of water.

D. all the above.

4.Which of the following statements can be the best title of the passage?

A. Teaching from the Sky.   B. Teaching on Physics.

C. Teaching Experiments.     D. Teaching by an Astronaut.