听力原文：M: It looks like we are going to have a shower at any minute now. W: I think so too. Isn' t it strange how you cart sense it. M: I know what you mean. W: Look at the clouds in the sky. Whenever they seem dark and law like this, you know it' s going to rain. Or look at an object that' s far away. If it seems clear to you, it probably going to pour. M: Yes, and every thing seems to have a stronger smell to me then. W: I know, and people often say it' s going to rain when they have aches and pains in certain parts of their body. M: mother always complains that her knee hurts just before a storm. M: And have you ever noticed how the animals act before a storm? W: Sure. Horses and cows always seem to go to a protective area and huddle together. M: Yeah, but with always the sensible things, how come we aren't carrying an umbrella with us now. What is the main topic of the conversation?