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present simple, present perfect For some years the community (1)
encourages / has encouraged collaborative clinical trials. In this section we (2)
describe / have described the first of two unreported results on such trials that we believe deserve such publication. Then, in Section 2, we (3)
review / have reviewed the broad perspectives that (4)
shape / have shaped the direction of the literature on clinical trials. Section 3 answers the question Under what circumstances (5)
are trials / have trials been carried out since the introduction of the new norms. Finally, we (6)
draw / have drawn some conclusions in Section 4. We believe that this (7)
is / has Share with your friends: 
