'Tic-tac-toe' or 'cross & noughts'

Two amateur people are playing a game of tic-tac-toe. Each person places his/her mark, either X \color{#D61F06} X or O \color{#3D99F6}O. We do not know who started first.

After the first player has placed his/her second mark, the players will always place his or her mark in a line that already contains

(a) two of his/her own marks,
(b) two of his/her opponent's marks,
(c) giving priority to (a) over (b).

Only the last mark to be placed in the game shown in the figure has not been given. Who will win the game, X \color{#D61F06} X or O? {\color{#3D99F6}O}?


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