Directions: Read the following information carefully to answer the given questions:

A company wants to select a team of four call centre executives from its South Indian centre for transfer to North India where they are going to set up a new centre. The company is managed by professional managers and is very particular about human resources and personnel relations. There are seven team members of equal ability X, Y and Z (who are senior), and A, B, C and D (who are junior). The company requires that there should be two senior executives and two junior executives in the team. It is also necessary that all of the executives in a particular team are friendly with each other in order to have a real team spirit and avoid any personnel relations problem in the new centre being set up in the North. Following is the situation of relations among the seven executives. (i) Y and A are not friendly. (ii) Z and C are not friendly. (iii) A and B are not friendly.

[X.A.T. 2005; M.B.A. 2004]

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If both Y and Z are selected, which of the executives must be on the team with them?