Abstract: It is one of resource constrained project scheduling problems, which selecting 2\emph{m} activities from \emph{n} parallel activities to make \emph{m} ordinal activities pairs and minimize the affection on the project duration. In order to provide theories and methods for such problem, in this paper, we study the optimization problem that how to select eight parallel activities from \emph{n} ones to make four ordinal activities pairs. Based on present theory, optimal row-mate theorem is given, and founded on them, standard-criterion algorithm is designed and proved theoretically. Finally, an example is given to illustrate the feasibility of the algorithm.