我可以告诉你ABD都是没有错误的。这道题很中式化。如果一定要解释，参看朗文现代词典：
aware: if you are aware that a situation exists, you realize or know that it exists
aware和know是一个意思，直接意思是：知道……的存在。但用know是毫无问题的。如果在口语中，用know最好。
understand是理解、了解的意思。比如I understand your feelings.
其宾语也可为一件比较复杂，难以理解的事情。
朗文现代词典提供了类似的例句：
I understand that this treatment may not work.
所以understand也是符合语境的。
recognize: to know who someone is or what something is, because you have seen, heard, experienced, or learned about them in the past
所以recognize是不合适的，准确的中文翻译是“认出、识别出”
出题这道题老师很不负责，他想考aware但是却