Hello, I looked this up because it was interesting. 'Block', when referring to aircraft, is synonymous with 'version' similar to Windows 7, 8 and 10 It is used to help identify problems with specific aircraft. For example, if people report problems with F-16 block 60 than they will make improvements and then release an F-16 block 70

But which one option is relative ? I am lost. 9?

There are explanations as refer:  BLOCK (noun)   The noun BLOCK has 12 senses: 1. a solid piece of something (usually having flat rectangular sides) 2. a rectangular area in a city surrounded by streets and usually containing several buildings 3. a three-dimensional shape with six square or rectangular sides 4. a number or quantity of related things dealt with as a unit 5. housing in a large building that is divided into separate units 6. (computer science) a sector or group of sectors that function as the smallest data unit permitted 7. an inability to remember or think of something you normally can do; often caused by emotional tension 8. a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope 9. a metal casting containing the cylinders and cooling ducts of an engine 10. an obstruction in a pipe or tube 11. a platform from which an auctioneer sells 12. the act of obstructing or deflecting someone's movements.