To match the pattern "pat" at the beginning of a line using the `grep`

command, the symbol `^`

will be used.

Now let's go through each option and explain why it is right or wrong:

A. ^pat: This option is correct. The `^`

symbol in a regular expression is used to match the pattern at the beginning of a line. Therefore, `^pat`

will match the pattern "pat" at the beginning of a line.

B. $pat: This option is incorrect. The `$`

symbol in a regular expression is used to match the pattern at the end of a line. Therefore, `$pat`

will match the pattern "pat" at the end of a line, not at the beginning.

C. pat$: This option is incorrect. The `$`

symbol in a regular expression is used to match the pattern at the end of a line. Therefore, `pat$`

will match the pattern "pat" at the end of a line, not at the beginning.

D. pat^: This option is incorrect. The symbol `^`

does not have any special meaning when it appears after the pattern. Therefore, `pat^`

will match the literal string "pat^" rather than the pattern "pat" at the beginning of a line.

The Answer is: A. ^pat