In the pre-modem era, the sale of surplus food took place once a week when farmers took wares on market day, into the local village marketplace.中 when farmers took wares on market day, into the local village marketplace.是时间状语.into前为什么要加，？直接写成 when farmers took wares  into the local village marketplace on market day也能表达清楚作者意思。为了强调 on market day集市日吗？