The trip to the Mystery Caves will take place on Sunday, 27 July. You can book your tickets in Room 188 between 2:30 p.m. and 4:00 p.m. every day. Your parents should confirm (确认) the booking by writing to us as soon as possible. You should pay for the trip before 21 July. If we do not receive your money early enough, your booking will be cancelled(取消). If the trip does not take place for any reason, your money will be paid back.
We are planning to meet outside the railway station on Black Street at 8:00 a.m. It will take us about 2 hours to get to the center of the town by train, and from there we have to catch a bus. It will take another hour to get to the Mystery Caves on the bus.
We will spend about 1 hour and a half visiting the caves (山洞), and we hope to catch the 1:30 bus to Happy Lake for some swimming. If we are late, we will have to take the 3:00 bus straight back to Black Street.

If you miss the 1:30 bus to Happy Lake, you will
[A] have to go back by train
[B] not be able to go swimming
[C] go to the lake on foot

某城市注重生态文明的建设，建立人工湿地，形成藻菌共生污水净化系统，对生活和工业污水（主要含有机物）进行净化处理。

人工湿地中的芦苇属于挺水植物，绿藻属于浮游植物，黑藻属于沉水植物，这种垂直结构显著提高了群落（）等环境资源的能力。人工湿地中菌类等作为分解者的作用是（），此过程中还可产生二氧化碳，有利于藻类等植物光合作用中（）的进行。