A、It is made of aluminum. B、It is too heavy to hand. C、It is strongly built. D、It is in the art museum. A女士说移动雕塑全是用铝做的，所以它不会砸到人的

M: How do you like the new art museum?
W: Wonderful! I spent most of my time at the art museum. I especially liked the new wing. I was amazed to hear the guide explain the problems they had building it.
M: Right. [12]I just read an article that went on and on about the cost. 90 million in total I think.
W: Yeah. The guide mentioned that. You could see they spared no expense.
M: Hm. It looked really unusual, at least from what I saw in the picture.
W: It is. [13]The basic design is two triangles. In fact there are triangles all over, the paving stones in the courtyard, the skylights and even a lot of the sculptures. One sculpture is a mobile. It’s in the courtyard and it’s made of pieces of aluminum that moves slowly in the air. It’s really impressive.
M: That was in the article too. [14]It said that the original was steel and it weighed so much that it wasn’t safe to hand.
W: Right. [15]They did it over in aluminum so it wouldn’t come crashing down on someone’s head.
M: You know the article went into that in detail. There was even an interview with the sculptor.
W: I’d like to read that. Would you mind if I borrow the magazine sometime?
M: No. I wouldn’t mind if I haven’t thrown it out yet.
12. How had the man learned about the museum?
13. According to the woman, what do the paving stones and skylights have in common?
14. What was the problem with the original mobile?
15. Why wouldn’t the mobile crash down on someone’s head?