Portia，for physics had once been very hard，turned out to be a physicist.A. whomB. whoseC.

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A. whom
B. whose
C. that
D. which
解析：for whom(对她来说)引导一个非限定性定语从句，补充说明主语Portia。在介词后面只能用which或whom，不能用that。题干中如果没有for，则应该选whose。