If we can lock a file, we can solve the race condition problem by locking a file during the check-and-use window, because no other process can use the file during the time window. Why don’t we use this approach to solve the race condition problems discussed in this chapter?

A file can only be locked out to other users or processes only if it's already open, meaning it's in use as a resource during the time window and therefore it's impossible solving the race condition problem by locking the file during the check-and-use window.

Hence, during the check-and-use process, it's impossible to lock a file.

In conclusion, any lock created can be ignored by the malicious process.

the correct answer is a) her connection with a character

this is correct on edgnuity : )