We need the word "but" to contrast the first part of the sentence (which describes a similarity) with the second part (which describes a difference). B and D are out.
A is wrong because we don't want to compare the English to "the French that considered their colonies part of France itself." We want to compare the English to the French. If we changed "that" to "who," and used a comma to separate, we would have a non-essential modifier and the sentence would
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A is wrong because we don't want to compare the English to "the French that considered their colonies part of France itself." We want to compare the English to the French. If we changed "that" to "who," and used a comma to separate, we would have a non-essential modifier and the sentence would
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