Researchers have discovered that dolphins are able to mimic human speech.（）

单项选择题When insects feed on decaying plant material in a compost pile, they help turn it into useful garden soil.（）

A．available
B．organic
C．distasteful
D．decomposing

单项选择题As a conductor, Leonard Bernstein is famous for his intensely vigorous and exuberant style.（）

A．enthusiastic
B．nervous
C．painful
D．extreme