From 2004 to 2005, Unlimited Postal Service had the highest on-time overnight delivery rate of the six major delivery companies in the country. From 2005 to 2006, however, Unlimited Postal Service had the lowest on-time overnight delivery rate of the six major delivery companies. The on-time overnight delivery ranking of the other five companies relative to each other remained unchanged.

Which of the following, if true, would most contribute to an explanation of the facts above?

a) In early 2005, Unlimited Postal Service stopped taking overnight deliveries after 1:00 PM to ensure that the deliveries would be made according to schedule.
b) In a drastic cost-cutting measure, Unlimited Postal Service laid off 10 percent of its employees in early 2005.
c) Unlimited Postal Service implemented a new electronic package tracking system in early 2005 in order to improve delivery speed and efficiency.
d) In response to cuts to their retirement benefits, Unlimited Postal Service's delivery personnel went on a company-wide strike for all of February 2005.
e) Although all six delivery companies try to keep their overnight deliveries on schedule, increased security measures at many airports increased delays in deliveries originating in the cities those airports serve.

I am confused between two close options... Not able to narrow down between b and d