Which of the following commands will find the string foo in the file filel M, regardless of foo being in upper or lower case letters?

Which of the following commands will find the string foo in the file filel M, regardless of foo being in upper or lower case letters?

A.
grep-i foo | file 1 .txt

B.
grep-nfilel.txt<foo

C.
grep-nfoofile1.txt

D.
cat file 1.txt > grep-n foo

E.
catfilel.txt| grep-ifoo