alternately
  (ad.)交替地,隔一個地
  Al·ter·nate·ly adv.
  1. In reciprocal succession; succeeding by turns; in alternate order.
  2. Math. By alternation; when, in a proportion, the antecedent term is compared with antecedent, and consequent.
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  alternately
       adv : in an alternating sequence or position; "They were
             deglycerolized by alternately centrifuging and mixing";
             "he planted fir and pine trees alternately"