The naughty boy had wanted to play football with the kids in the street, but his parents warned him .
A. not to
B. not to do
C. to do
D. of doing
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(答案→)A. not to
B. not to do
C. to do
D. of doing
解析：考查不定式的省略：句意：调皮的男孩想和街上的孩子踢足球，但是他的父母警告他不要（踢球）。这是省略句，完整的是his parents warned him not to play football。不定式的动作如果前面出现了，可以省略动词do，但是to要保留。选A。