While working with MS-DOS which command is used to combine file1 plus file2 into new file named file3?

To combine file1 and file2 into a new file named file3 in MS-DOS, you would use the copy command with the + symbol to concatenate files. Here’s how each option works:
Option A: Copy file3 file1+file2 attempts to copy file3 as a combined file of file1 and file2, which is incorrect.
Option B: Copy file1+file2 file3 correctly combines file1 and file2 into a new file named file3.
Option C: Copy file1+file2+file3 does not follow the correct syntax for combining files in MS-DOS.
Option D: Copy file2 file1+file3 attempts to copy file2 and rename it to file1+file3, which is not the operation to combine files.
Therefore, Option B is the correct command to combine file1 plus file2 into a new file named file3 in MS-DOS.