21. — What do you think of the grammar book?
— Oh, it really is ________ useful reference book, which is worth reading ________ second time.
A. a; a B. an; the C. an; D. the; the
22.She tried her best to ________ the life there，but failed to make any ________.
A．adjust to；sense B．adapt to；trouble C．adapt to；effort D．adjust to；difference
23.On the ground ___________ a sick goat, whose life was in danger.
A. lay B. lays C. lying D. laying
