has been to 曾经，为什么要加个to

title: has been to
date: 2018-08-22 09:53:46
NO_sents: 323
NO_references: 182

has been to

• The purpose of this paper has been to press the argument that considerable thought will be necessary before paternity probabilities become a useful tool for legal proceedings. (Aickin, 1984)
• A third approach in researching dehydration tolerance has been to use species important to agriculture to analyze the plant response after drought stress. (Ingram, Bartels, 1996)
• In almost all cases, the aim has been to provide a complexity measure that allows models' comparison and selection (via, for instance, the AIC). (Rodríguez-álvarez et al., 2016)
  
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