Which of the following commands will find the string foo in file1.txt, regardless of foo being in upper or lowercase letters?

A.
cat file1.txt | grep -i foo

B.
cat file1.txt > grep -n foo

C.
grep -i foo | file1.txt

D.
grep -n file1.txt < foo

E.
grep -n foo file1.txt

Explanation:
grep option -i tells grep to work case insensitive.