Let's analyze each situation presented in the question to determine the correct answer.

1. Situation A: "Growth and branching of roots in the A-horizon and B-horizon is advantageous for absorption of water and minerals."
   • The A-horizon of soil, known as the topsoil, is where most biological activity occurs. It is rich in organic material and nutrients, making it ideal for root growth and for plants to absorb water and minerals.
   • The B-horizon, or subsoil, lies beneath the A-horizon. It often has less organic material but is important for the storage of minerals leached down from the topsoil.
   • Roots growing and branching in these horizons can indeed enhance the absorption of water and minerals, supporting plant growth.
2. Situation B: "C-horizon is rich in humus which makes soil soft and porous."
   • The C-horizon is the layer of soil that consists mostly of weathered parent material and is located beneath the B-horizon.
   • It is generally devoid of humus compared to the A-horizon, which is why it is often not soft and porous. Instead, it acts as a transition layer to the bedrock.
   • This statement is incorrect because the presence of humus is characteristic of the A-horizon, not the C-horizon.

Based on this analysis, Situation A is true, and Situation B is false. Therefore, the correct answer is: Only Situation A is true.