未知题型 突触在结构上可分为两部分，即突触前部分和突触后部分。( )

未知题型 Older people are generally advised to _____.(A) keep fit by going in for physical activities(B) keep mentally active by challenging their brains(C) maintain mental alertness through specific training(D) maintain a balance between individual and group activities

问答题 河北北方学院2012年6月英语四级报名费是多少啊？