Which permissions are set on a regular file once the permissions have been modified with the command chmod 654 file.txt?

The leading 'd' indicates a directory, not a regular file, so this string cannot represent the result of chmod on a regular file.

A leading 'd' again incorrectly designates a directory, and the bits -wxr-x-- do not correspond to the octal values 6, 5, and 4.

Standard Unix permission strings contain exactly 9 permission bits after the file-type character; a trailing standalone 'r' in position 10 is syntactically invalid.

The others field shows '-r--x' which would be octal 5, not octal 4 as required; the correct others bits for digit 4 are r-- (read only, no execute).

The leading '-' denotes a regular file. Octal digit 6 (binary 110) assigns the owner rw-, octal 5 (binary 101) assigns the group r-x, and octal 4 (binary 100) assigns others r--. Combining the file-type character with the three permission triplets produces the string -rw-r-xr--, which matches choice E exactly.