A sequence of transformations is described below.
A reflection over a line \overleftrightarrow{PQ}
PQ

P, Q, with, \overleftrightarrow, on top
A translation
A reflection over another line \overleftrightarrow{RS}
RS
R, S, with, \overleftrightarrow, on top
A dilation about a point TTT
Which of the following must be preserved under this sequence of transformations?