static S ai_guessVerb(S s) {
  S a = firstWord(s);
  if (a == null) null;
  if (ai_yesNoQuestionWord_1(a) && neqicOneOf(a, "am", "are", "is")) {
    s = dropFirstWord(s);
    try answer appendIfNempty(tripleB(splitAtBaseFormVerb(s)), "?");
  }
  null;
}