Read the excerpt from Roll of Thunder, Hear My Cry.

I had gotten as far west as the Dakotas when my silent recitation was disturbed by a tapping on the porch. I lay very still. Mr. Morrison never made sounds like that.

Which detail from the excerpt best helps the reader determine a tone of alarm?

I had gotten as far west as the Dakotas
my silent recitation
a tapping on the porch
Mr. Morrison never made sounds like that.

The detail that best helps the reader determine a tone of alarm is "a tapping on the porch."