题目

My sister is expecting me,____ I must be off now.        A. however           B. or              C. so             D. otherwise 答案：C已知集合A={x|3≤x＜6}，B={x|2＜x＜9}．（1）分别求：∁R（A∩B），（∁RB）∪A；（2）已知C={x|a＜x＜a+1}，若C⊆B，求实数a的取值集合．