Read the following text carefully and choose the correct answer A, B, C or D for each of the gap.

When you are in Singapore, you can go about (11) taxi, by bus, or by underground. I myself prefer the underground (12) it is fast, easy and cheap. There are (13) buses and taxis in Singapore and one cannot drive along the road (14) and without many stops, especially on Monday morning. The underground is therefore usually quicker (15) taxis or buses. If you do not know Singapore very well, it is difficult (16) the bus you want. You can take a taxi, but it is (17) expensive than the underground or a bus. On the underground, you find good maps that (18) you the names of the stations and show you (19) to get to them, so (20) it is easy to find your way.