be able to 的陈述句用be动词放句首.用do是画蛇添足,既麻烦又不地道.例如：He is able to jump high.（他能跳得很高）提问：Is he able to jump high?（他能跳得很高吗）able（能够..的）是形容词,跟在be动词后,有be...