watering本题有关垂直花园的评估状况。录音原文提到这些外墙需要大量洒水(so much watering)，其中so much watering对应题目中的constant“经常的”。再结合前文提到的watering five times a day

(Frank=F Sherry=S)
F: Hi Sherry, how are you?
S: Fine, Frank, but this assignment’s taking longer than I’d hoped.
F: Yes, it’s quite detailed.
S: Designing two small vertical gardens doesn’t seem too hard, but there’s so much stuff online about large-scale projects that reads like propaganda.
F: I know what you mean. Vertical gardening is flavour of the month, when all it amounts to is growing plants on surfaces not used in the past.
S: Tricky surfaces at that.
F: Yes. Walls do present challenges.
S: Vertical gardening is popular in warmer climates, and where there’s cash to spare. I can’t see people in my country adopting it, or indeed anyone who doesn’t own their own home — all that construction effort, then watering your plants five times a day. How ever would you transport your wall if you moved?
F: We should certainly include your concerns at the end of our presentation when we assess whether vertical gardening will become a design fundamental or remain a passing fad.
S: OK. How are we going to divide up the presentation? I’m happy to do the second part.
F: Our domestic designs?
S: Yes. I’m afraid I can’t get interested in the large-scale works, like the wall at the Caixa Forum Museum in Madrid — they seem gratuitous to me.
F: Don’t worry, I’ll comment on them. However, I do think the vertical garden in the Rue d’Alsace in Paris is amazing. It’s like having a vast mossy forest floor stood up on its side amidst all the concrete and tar-seal.
S: So we just need to work on the first part together — the history of the movement and the reasons for its growth. I read that a French botanist, Patrick Blanc, invented vertical gardening in 2008.
F: And I read that he got the idea from tropical rainforests in Malaysia, where plants grow at any height, and their superficial root systems don’t need any soil.
S: Still, I don’t understand why the movement took off, and companies from Sydney to Tokyo com-mission him to cover walls with plants, especially when the walls need so much watering.
F: I suppose businesses want to show how green they are.