Bookseller sends Reader an unsolicited book with an invoice for it. Reader, knowing nothing about Bookseller, ignores both the book and the invoice. Has Reader accepted the book and therefore is obligated to pay the invoice?

No. Silence is never acceptance.

No. Communication is always required and Reader did not respond.

Yes. Since Reader has the book, he must pay the invoice.

Yes. Consumers must always pay for goods they receive.

No. Silence is not acceptance when Reader has not used the book.