Which of the Following Designs Would Probably Be Highest in Internal

Multiple Choice

Which of the following designs would probably be highest in internal validity?

A) Y1      X      Y2
B) X       Y2
$\quad$ ---     Y2
C) (R)      X      Y2
$\quad$ (R)      ---     Y2
D) Y1      X      Y2
$\quad$ Y1      ---     Y2