When the author recalls Harlem in the old days, he has a feeling of

单项选择题The American Constitution, the oldest written one in the world, started to take effect in

单项选择题The early warning systems developed in the 1990's are used to

单项选择题After the Parkfield programme, experts concluded that earthquake prediction in terms of days and years was

单项选择题The ambitious Parkfield programme was successful at least in one of the following aspects:

单项选择题Harlem was called the capital of Black America in the 1920s and '30s mainly because of its