身处教育实践第一线的研究者与受过专门训练的科学研究者密切协作，以教育实践中存在的某一问题作为研究对象，通过合作研究，再把研究结果应用到自身从事的教育实践中的一种研究方法是().

单项选择题The singer and the dancer () come to the meeting.

A．has
B．have
C．are
D．is

单项选择题Can you() who has lost the watch

A．look for
B．look up
C．find
D．find out

单项选择题The meaning of the sentence is (); you can interpret it in several ways.

A．skeptical
B．intelligible
C．ambiguous
D．exclusive

单项选择题Is () necessary to complete the design before National Day

A．this
B．that
C．it
D．he

单项选择题All but one () here just now.

A．is
B．was
C．has been
D．were