Final answer:
In the given sentence from the context, the most appropriate word to fill in the blank is 'tacit', which means understood or implied without being directly stated, fitting Calpurnia's non-verbal nod of agreement.
Step-by-step explanation:
The best option to fill in the blank in the sentence 'Jem went in grinning, and Calpurnia nodded _____ consent to having Dill in to supper.' is (C) tacit. This means that her consent was understood or implied without being directly stated. While all the options are adjectives that describe types of consent, 'tacit' consent would be the kind that is unspoken yet understood, fitting the context where Calpurnia nods without verbal confirmation.
Options (A) 'reserved' and (D) 'explicit' are less fitting because 'reserved' would imply hesitancy, and 'explicit' would mean clearly stated, which contradicts the nodding action. Option (B) 'enthusiastic' is also less appropriate, as the context does not indicate an excessive display of enthusiasm.