已知圆柱的底面半径为3cm，母线长为5cm，则圆柱的侧面积是（    ）

    Singapore's public transport system is one of the best in the world, so you should have no problem finding your way around like a local. There are three main forms of public transport that you would find in any other major city—trains, buses and taxis.

    TRAINS

    Trains run from 6:00 am to midnight. Single trip tickets start at 80 cents. If you buy an EZ-Link cars for $15, you can ride the trains and buses as you like.

    If you need more information, just call Transit Link on 1800 525 7333.

    BUSES

    There are several bus services in Singapore and fares start at 80 cents. Be sure always ask the driver the cost of your ticket as he can not give change.

    If you need help, just call Transit Link on 1800 525 7333.

    TAXIS

    There are three main taxi companies—City Cab (6552 2222), Comfort (6552 1111) and Tibs (6552 8888). Booking can also be easily by calling the numbers listed above.

    RENTAL CARS

    Driving in Singapore is a pleasure and if you liked to travel at your own pace, renting a car is a good choice. Renting takes away the hassle of getting to places around Singapore. Just sit back and enjoy the city. It also means you'll get to see a lot more that a train or a bus won't let you see.

    For car rental, call Avis on + 65 6737 1668.

设数列{a_n}的前n项和为S_n，令$T_n=\frac{S_1+S_2+...+S_n}{n}$，称T_n为数列a₁，a₂，……，a_n的“理想数”，已知数列a₁，a₂，……，a₅₀₀的“理想数”为2004，那么数列2，a₁，a₂，……，a₅₀₀的“理想数”为（     ）

关于扩音机的作用，下列说法中正确的是 (     )