A:全球剧变令人忧虑
B:世界联系日益密切
C:国家之间对抗激烈
D:民族矛盾逐渐缓和
As students, you must listen to the teacher attentively and keep a record ______ what the teacher says in class.
当a =____时,分式 a+3a−2 的值为-4.