39._____ participation in public decision-making,telephone c

39._____ participation in public decision-making,telephone conference calls are widely used.A.E
39._____ participation in public decision-making,telephone conference calls are widely used.
A.Extend B.Extending C.To extend D.Having extended
类比这题：
_______ for another two miles,the park borders a lake and ensures more clear air for the city as a green lung.
A Having extend B Being extended C Being extended D Extended