The most obvious effect of pressure on rocks is

foliation
lineation
lithification
the reorientation of mineral crystals

The correct answer is D. the reorientation of mineral crystals.

Pressure is a force that is applied evenly over a surface. When pressure is applied to a rock, it can cause the mineral crystals in the rock to reorient themselves. This is because the pressure causes the crystals to deform, and the deformation causes them to align in the direction of the pressure.

Foliation is a type of rock fabric that is characterized by the alignment of platy or elongate minerals. Lineation is a type of rock fabric that is characterized by the alignment of elongated minerals or elongate features in the rock. Lithification is the process by which sediment is converted into rock.

The reorientation of mineral crystals is the most obvious effect of pressure on rocks because it is the most visible. The other options, foliation, lineation, and lithification, are also effects of pressure, but they are not as obvious as the reorientation of mineral crystals.