It is not always easy for the public to see _______ use a new invention can be of to human life.

A．whose            B．which            C．that              D．what

 The sunspot came into its active stage, __________ that happens once every eleven years.

A．one              B．it                C．the one           D．what

It was on September 25^th ______ China’s first aircraft carrier, named “Liaoning”, was handed over to PLA Navy.

A．when            B．who              C．that              D．what

The tourists can not help wondering ______ the ancient people could manage to complete the magnificent building without modern equipment.

A．that              B．how              C．where            D．what

---We could invite John and Barbara to the Friday night party.

---Yes, _______? I’ll give them a call right now.

A．why not           B．what for           C．why              D．what