There was _____ accident outside our school this morning.
accident 是以元音音素开头的单词，此处表泛指，故用 an。
— Lily,what will you do if you meet some crimes?
— I must call the police for help _____.
四个选项的含义分别是：in time 及时；on time 按时；all the time 一直；by the time 截止到……。根据本题语境可知，当你遇到犯罪行为的时候，要及时报警，故答案为选项A。