When does the songbird perform a tap dance?

In this section， you will hear five short news items.
Each item will be read only once.
After each item， there will be a fifteen-second pause.
During the pause， read the question and the four choices marked A， B， C and D， and decide which is the best answer.
Then mark the corresponding letter on the answer sheet with a single line through the centre.
16. Scientists have discovered the species of songbird performs a tap dance so fast that it can’t be seen by the naked eyes. Researchers from Japan and Germany slow down footages of the blue capped cordon-bleu songbirds during courtship. Scientists have discovered that tap dance is in the courtship performance of both male and female cordon-bleus. The next step for the researchers is to try and pick whether the birds mate is moved by the sight， the sound or the vibrations of this fancy foot work. Such is the agility of the songbirds show stopping quickstep that could only be fully appreciated in super slow-motion.
17. Israeli officials say the government will approve about 500 new buildings in the West Bank settlements in the coming days. Israeli Cabinet ministers announced their support for the plan on Sunday. Defense Minister Ehud Barak will officially give approval for the new housing within 48 hours. The plan also would permit existing settlement building to continue.
18. Sri Lanka’s Tamil Tiger rebels have admitted defeat in fighting against government troops， the rebels said they would lay down their arms to prevent what they called “further unnecessary killing of Tamil civilians by government troops”. The government said it has succeeded in its goal to defeat terrorism and rescue all civilians from terrorism after a 26-year long civilian war.
19. Australia has joined a growing international appeal for aid to Somalia where much of the population is starving. Australian Foreign Minister Kevin Rudd spoke in Somalia. He said hundreds of thousands of Somalis， mostly children will die if the international community fails to provide aid.
20. It suggests walking， cycling or travelling by public transport can lift the mood. Crucially， it suggests those who switch from the car to an active commute feel better across a range of psychological measures， including concentration， decision-making and the ability to face up to problems. The researchers say policies encouraging people to leave their cars at home could have a dramatic impact on public wellbeing.