It appears you've provided a list of options related to various processes or actions, likely related to biology or physics. However, you haven't specified what you're asking for. Each option describes a different concept:
a. Conversion of mechanical energy into radiant energy: This refers to a physical process where mechanical energy (like movement) is transformed into light energy (radiant energy). An example is how a moving object can produce light when it generates friction.
b. Action of contractile fibers: This typically describes muscle contraction, where fibers in muscle tissues (like actin and myosin) interact to produce movement.
c. Conversion of light energy into heat energy: This process is often seen in photosynthesis, where light energy is absorbed by plants and can be converted to heat, among other forms of energy.
d. Action of plant hormones: Plant hormones (such as auxins, gibberellins, and cytokinins) regulate various growth processes in plants, influencing growth direction, flowering, and fruiting.
If you have a specific question or need clarification on any of these points, please let me know!