纠结到心碎（苦

Since the start of the space age, more and more littering has occurred in orbits near Earth, often becausethe intentional discarding of lens caps, packing material, fuel tanks, and payload covers.

• Amore and more littering has occurred in orbits near Earth, often because  分析A选项
• Borbits near Earth have become more and more littered, often from  分析B选项
• Corbits near Earth became littered more and more, often resulting from  分析C选项
• Dthere have been more and more littering of orbits near Earth, often because of  分析D选项
• Ethere had been littering more and more of orbits near Earth, often with  分析E选项
• 这题选B不难，但我纠结的是D选项中there be的谓语单复数形式，是根据littering还是orbits？
• 跟这个问题类似的纠结点还有the n. of  n. that/which的修饰问题，是修饰of之前的还是of 之后的呢？