Final answer:
The correct answer is option d) Mark's computer does not have the same program you used to write the proposal.
Step-by-step explanation:
Based on the information provided, the most likely reason that Mark cannot open the newly created sales proposal is because Mark's computer does not have the same program you used to write the proposal. This is a common issue related to software compatibility, where newer versions of software can open files created in older versions (upward compatibility), but the reverse is not true.
Therefore, if you have used a newer version of a program to create the file, and Mark has an older version of the program, he would not be able to open the file until he upgrades to a newer version of the program.
To resolve this, you might need to save the proposal in a format that is compatible with older versions of the program or use a different program to create a version that Mark can open. Another option is to check if Mark can update his software to a newer version that can handle the file format used by your proposal.