56．If you are interested in rock formations, which activities are the best choices?
A．Caves and Fossils． B．Fossils and Manners．
C．Caves, and Exploring Caves． D．Exploring Caves and Manners．
57．If you are members' friends, what benefits can you receive?
A．Two free lectures every month．
B．A membership card and certificate．
C．Favourable price for Youth Camp．
D．Two free tickets to Echo Cove Cave．
58．The purpose of this poster is to invite more people to ______．
A．join the Cave Club B．enjoy the underground world
C．work as volunteers, D．protect the educational caves