It's quite obvious that the aging population in China will cause        heavy pressure on            ________ whole society in the future．

A．／；the         B．the；／         C．a；the        D．a：a

On seeing_____ gift they wanted, the kids screamed with _____ delight.

A. /;  a           B. a;  the       C. the;  /           D. the;  a

 _____ new cure for this disease that medical experts have recently developed proves to be ______ most effective, although it can not completely kill all the viruses.

A. A; a        B. The; /             C. /; the                   D. A; the

Remember to take a breath of ______ fresh air and have some exercise each day. It will make ______ difference.

A. /；a                                 B. the；a                     C. /；the                            D. a；the

According to ______ survey，there're more and more young people who go for a walk at ______ dusk instead of sitting in front of the computer.

A. a；the                  B. a；不填                 C. the；the          D. 不填；不填