China’s new food law provides for a food recall （召回） system ______ producers have to stop production if their food isn’t up to standards．

A． where         B． that          C． when          D． which

（2010·江苏宝应中学高三上第一次学情调查）    33. China’s new food law provides for a food recall（召回）system ______ producers have to stop production if their food isn’t up to standards.

A. where           B. that        C. when            D. which