Compose with $g=(f-i/2)/(f+i/2)$, which maps D to D and fixes zero. Schwarz’s lemma bounds |g′(0)|≤1; differentiation at f(0)=i/2 gives |g′(0)|=|f′(0)|. Equality is attained by f(z)=(i/2)(1+z)/(1−z). Thus **1, C**.
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