There was so serious a matter that I had no choice but the police.
A. called in
B. calling on
C. call for
D. to call in
网友回答
A. called in
B. calling on
C. call for
(答案→)D. to call in
解析：考查短语：别无选择做某事have no choice but to do,句意：有如此严重的事以至于我别无选择给警察打电话。所以选D。