Answer:
a. Employees interested in enrolling their children in our new low-cost day-care program are invited to attend an HR orientation on January 18.
Step-by-step explanation:
Subject line: HR orientation regarding new day-care program.
The problem with message (b) is that it is not direct and includes a lot of information that should go further down the email, not as an opener. Information regarding previous options or how difficult this project do not belong here.