东欧旅行社:句中出现up to now用什么时态？

句中出现up to now用什么时态？ From The First Up To Now什么意思 from now on,from then on分别用什么时态 right now,just now分别用在什么时态,各是什么意思? just now ,so far , up to now 是什么意思 Does tom go to school now ?这是什么时态 为什么 Now and then ___ up to see what happened. We need to line up .(同意句) l am going to go out now 。这句话有时态问题吗？ I have been to shanghai 什么时态