A、Jellyfish. B、Oceanic snails. C、Different plants. D、Sunken treasures. B文中提到他们在海洋蜗牛的身上喷了一种绿色染料，所以照片中显现出了绿色的轮廓。

W: Hi, Tom.
M: Hi, Judy. Haven’t seen you for weeks. Where have you been?
W: In Florida.
M: (2)Vacationing while the rest of us have been studying on campus in the February cold?
W: (1)Not exactly. I spent most of my time underwater.
M: I don’t understand.
W: (3)I was on a special field trip. I went with my marine biology class.
M: So you went deep water diving. What were you looking for, sunken treasures?
W: You might say so. The sea is full of treasures, all kinds of strange fascinating organisms. Our class concentrated on studying plankton, which is a small form of plant and animal life living in water.
M: I thought plankton is too small to be seen.
W: That’s a common misconception. The term plankton covers a very wide variety of freely floating plants and animals.
M: I hear most plankton is transparent, aren’t they?
W: Yes. Most plankton has transparent tissues as a protective disguise, such as jellyfish. 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 plants and animals.(4)In fact, our professor even took photographs of Greeber Quadam, which are small oceanic snails.
M: How will the snails show up in the photographs if they are transparent?
W: We sprayed Greeber Quadata with a harmless green dye. Since particles of the dye stuck to their tissues, the snails appeared in green outline in the photographs.
M: That sounds like all 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.
Questions 1 to 4 are based on the conversation you have just heard.
1. How did Judy spend most of her time in Florida?
2. What was Tom doing in February?
3. What kind of class went on the field trip?
4. According to Judy, what did her professor photograph?