数据库功能可分为前端和后端。下列叙述错误的是______。

A．后端负责存取结构、查询计算和优化、并发控制以及故障恢复

B．前端包括表格生成器、报表书写工具、图形用户界面工具等

C．前端与后端之间通过过程化语言来接口

D．在集中式系统中，前端和后端在同一个系统中运行

We all know that we ________ our carbon footprint, but I suspect that many people wouldn't be prepared to go as far as Joan Pick, a retired scientist living in south London.

A．must have reduced

B．should have reduced

C．may have reduced

D．could have reduced