The correct answer is hydraulic prop. Here's why:

• Active Support: Active support systems are designed to exert immediate and continuous resistance against strata movement. They actively work to prevent or minimize deformation. Hydraulic props fall under this category as they provide an immediate and adjustable load-bearing capacity right after installation and as the roof moves.

• Passive Support: Passive support systems rely on the strata to deform before they become fully effective. They resist movement after it has already begun. Let's look at why the other options are passive:

  • Wire Mesh: Primarily used for surface support to prevent small rock fragments from falling. It doesn't actively resist strata movement.
  • Shotcrete: Provides a surface coating that consolidates the rock mass and prevents weathering. It gains strength over time and reacts to deformation rather than actively preventing it.
  • Fully Grouted Roof Bolt: Stabilizes the rock mass by tying together layers of rock. The bolts need deformation to be fully effective by mobilizing the shear resistance between the layers.