A．there is B．it were C．there was D．it was
单项选择题Volcanoes (火山)（）as active, dormant and extinct.
A．described B．are described C．being D．which are described
单项选择题I would have come sooner but I（）that you were waiting.
A．wouldn' t know B．didn' t know C．haven' t known D．don' t know
