问题补充：
When I talked with my grandma on the phone, she sounded weak, but by the time we up , her voice had been full of life.
A. were hanging
B. had hung
C. hung
D. would hang
答案：
A. were hanging
B. had hung
(答案→)C. hung
D. would hang
解析：考查时态。根据her voice had been full of life，说明by the time后面使用过去时。Hang up挂断电话。句意：等到我们挂断电话的时候，她的声音充满了活力。故C正确。
