Unlike competitive running , race walkers must always keep some portion of their feet in contact with the ground（）.

单项选择题Furniture makers use glue to hold joints together and sometimes to reinforce it（） .

A．its
B．fast
C．hard
D．them

单项选择题New York City surpassed the other Atlantic seaports in partly because it developed the best transportation links with the interior of the country（）.

A．part
B．partial
C．partner
D．parting