听力原文：W: Hi, Tom!M: Judy. I haven't seen you in weeks.Where have you been？W: In Florida
听力原文：W: Hi, Tom!
M: Judy. I haven't seen you in weeks. Where have you been？
W: In Florida.
M: What vacationing! While the rest of us studying on the campus in February cold？
W: Not exactly. I spent most of my time under water.
M: I don't understand.
W: I was on a special field trip. I went with my marine biology class.
M: So you went scuba diving. What were you looking for？ Sunken treasure？
W: You might say so. The sea's full of treasures. All kinds of strange fascinating organisms. Our class concentrated on studying plankton.
M: I found plankton were too small to be seen.
W: That's a common misconception. The term plankton covers a wild variety of freely flowing plants and animals, from microscopic one cell organisms to larger ones, such as the common jellyfish.
M: Jellyfish may be large enough to be seen. But they are transparent, aren't they？
W: Yes, most planktons have transparent tissues as protected camouflage, it makes them practically invisible to predators.
M: But not invisible to your biology class, I hope.
W: By concentrating, I was able to see the outlines of lots of different plankton plants and animals. In fact, our professor even took photographs of gastropods, which are small oceanic snails.
M: How would the snails show up in the photographs of their transparence？
W: We scoured it with harmless green dye since particles of the dyes stuck to their tissues, the snails appeared in green outline in the photographs.
M: That sounds like an interesting trip. But I think if I'd been in Florida in February, I'd much rather spend my time just swimming and lying in the sun.
(20)
A．She had her vacation there.
B．She took a diving course there.
C．She was there on a field trip.
D．She visited a marine exhibition.
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