未知题型 I would appreciate _____ it a secret.(A) your keeping (C) that you keep(B) you to keep (D) that you will keep

未知题型 What is the passage mainly about?(A) How biochemical changes occur in the human brain.(B) Why people should keep active not only physically but also mentally.(C) How intellectual activities influence brain-cell health.(D) Why people should receive special mental training as they age.

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