【正确答案】 D

【答案解析】本题是词汇题，考查根据上下文推测词义的能力。该词在第一段和第二段均出现过，从第一段“After three chapters are emailed，the installments stop，and those who want to keep reading can borrow the book at their public library or purchase it online．”可以推断出该词的意思。