Which of the Following Commands Will Reduce All Consecutive Spaces

Multiple Choice

Which of the following commands will reduce all consecutive spaces down to a single space?

A) tr '\s' ' ' < a.txt > b.txt
B) tr -c ' ' < a.txt > b.txt
C) tr -d ' ' < a.txt > b.txt
D) tr -r ' ' '\n' < a.txt > b.txt
E) tr -s ' ' < a.txt > b.txt