PREP 59

 A new genetically engineered papaya was produced not by profit-motivated seed companies, as was the case with most genetically
modified crops previously approved for commercial use, but by university and United States Department of Agriculture researchers who
allowed growers to use it free of charge.

这是这题的正确答案.

想请问一下as was the case...这个结构怎么解释?

中文解释：就如同（大多数转基因作物以前经过检验用于商业用途）的情况一样

至于语法结构我就解释不了了。。。语法功底太差，惭愧