'Negligence' means failure to take proper care of something or simply put, failure due to lack of alertness. Hence option D is the correct answer.
'Supervision' means the action of supervising or controlling someone or something; 'custody' means the protective care or guardianship of someone or something; 'superintendence' means the act or function of superintending or directing. Since none of these words means the opposite of 'watchfulness', options A, B and C are incorrect.