答：in time表示“及時(shí)”,指在約定的時(shí)間之前發(fā)生.
on time表示“準(zhǔn)時(shí)、按時(shí)”,指正好在約定的時(shí)間發(fā)生.如：
We hope you will arrive in time to attend the meeting. 我希望你能及時(shí)趕來(lái)參加這個(gè)會(huì)議.
They were just in time for the bus. 他們正好趕上了汽車.
The train came on time. 火車正點(diǎn)到站.
I’ll write to your father if you aren’t here on time tomorrow. 倘若你明天不準(zhǔn)時(shí)到的話,我就要寫信告訴你父親.