A、He couldn’t decide on a topic for his paper. B、He hadn’t heard from his family for some time. C、He thought the woman had been

M: Hi, Susan. Where have you been?
W: Hi, David. I was just at the library. I have to hand in my biology paper tomorrow.
M: Tomorrow? Oh, no[ I thought it wasn’t due until next week.
W: Oh. Don’t worry. It is due next Tuesday. But I’m going away for the weekend and won’t be back till Monday night.
M: Oh, where are you going?
W: Philadelphia. We’re having a family reunion. It’s my grandmother’s eightieth birthday.
M: Great! How many people will be there?
W: Around sixty.
M: It seems that your family are pretty close.
W: You said it. So have you started working on your biology paper?
M: Yeah. I’m doing it on bees and how they’re able to recognize whether another bee is related to them.
W: How can they tell?
M: They use their sense of smell. The bees guard their nests this way. If another bee approaches the nest, the guard determines if the new bee is familiar. If it is, it’s allowed to enter.
W: Sounds interesting. Can other insects do this?
M: Well, as far as I am concerned, some wasps can. Each wasp nest has a special combination of plant fibers and so the wasps that live there have a unique smell.
W: Urn, it sounds like that the bees are picky about who comes to their family reunion.