题目

数列{an}满足an=3an-1+3n1（n≥2），又a1=5，则使为等差数列的实数=_______． 答案：  1.When something ______________(worry) me, I always went to my mum for help when I was young.2.There__________________(be) a football match tonight, isn’t there?3.--- How often ___________ he _______________(write) to his father?--- Once a year.4.--- Where is Jim?--- He ________________(play) football over there.5.Can you hear the girl _______________(cry) in the next room?6.I’m sorry for _________________(knock) all your books onto the ground.7.If he _____________(tell) others my secret, I ______________(not make) good friends with him.8.He will do something _________________(work) out the problem for others.