More than fifty years after the Second World War, a number of African American soldiers were awarded―some of them posthumously―with the Congressional Medal of Honor, which was the nation’s highest military award, and which was long overdue in
recognition of their outstanding bravery.
Lets find the error in choice A. For this we need to understand the meaning of the sentence.
The sentence states the following:
1: Second world war + 50 years later - many African American soldiers were awarded a great Medal
2: This is called Congressional Medal of Honor
3: This is the nations highest military award.
4: This award was given to soldiers in long overdue recognition of their outstanding bravery.
Understanding the last point is the key to figuring out the grammatical error in choice A. What is the role of "long overdue in recognition of their outstanding bravery". The way it is written, it appears as though the Congressional Medal of Honor is long overdue in recognition of their outstanding bravery. This is not logical - how can a medal of honor be long overdue...The act of awarding that medal can be long overdue. That is the grammatical error - choice A uses "which modifier" to describe the action - awarded the medal. "Which modifier" can only be used for modifying nouns.
Hope this addresses your concern. The thing to keep in mind is - Always read the sentence and understand what the author is trying to communicate. (meaning analysis) Once you understand that, then you apply your knowledge of grammar and see if the author has used English language appropriately or not. (error analysis) Once you hone in on the errors, then you correct those errors. (answer choice analysis). The first step is always to understand the meaning.
If you skip this step, then you are setting yourself up for failure (especially for medium to difficult level questions).
What is the source of this question?