Hey there mate :)
As per question,
Question:- A software development team needs to upgrade a program, but the team members are having trouble understanding the program code and how it works. What could be the reason?
To find:- Write the correct option
Answer:- Option B. incomplete documentation
Answer per sentence:-
A software development team needs to upgrade a program, but the team members are having trouble understanding the program code and how it works. This is due to incomplete documentation.