What is the event that causes the speaker to reflect in "Dust of Snow"?

The speaker sees a pile of dust.

The speaker is caught in a snowstorm.

A crow flies from a hemlock tree.

O A crow knocks snow onto the speaker.

A crow knocked some snow down onto the speaker

This is the event that causes the speaker to reflect in the "Dust of Snow."

Explanation:

Robert Frost's poem "Dust of Snow," is about being optimistic. The poet was sitting under a Hemlock tree when a crow knocked down some snow particles on him. This simple incident struck a different chord of the poet's mind and changed his view about life completely. So he thinks it is ironic that a crow not related to goodness did a good deed and evoked the sense of finding positive in negative situations. This small event led to the shift of the poet's mood from hopelessness to hope.

the answer is a crow knocks snow onto the speaker.