What makes matters really bad for White is that Black pawns firmly control the center, restricting the movement of White's army.
or means:
What makes matters really bad for White is that Black pawns firmly control the center, which restricts the movement of White's army.
or means:
What makes matters really bad for White is that Black pawns firmly control the center, thus restricting the movement of White's army.
What makes matters really bad for White is that Black pawns firmly control the center, and restrict the movement of White's army.
This is somewhat hair-splitting. " modifies an implied "the fact that Black pawns control the centre". ".
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