题目

It's school time again! You're probably feeling excited and maybe a little sad that summer vacation is over. Some kids feel nervous or a little worried on the first day of school because of all the new things: new teachers, new friends, and even a new school. Luckily, these “new” worries only stay around for a little while. Let's find out more about going to a new school. Most teachers kick off the new school year by introducing themselves and talking about all the new things you'll be doing that year. Some teachers give students a chance to tell something about themselves to the r计算：（a-1b2）3=________．