Final answer:
Scaffolds must be supported by adequate firm foundations to ensure stability and safety. Loose, soft, or unstable grounds are unsuitable and can lead to accidents.
Step-by-step explanation:
The suitable foundation that scaffolds must bear on is B) Adequate firm foundations. Scaffoldings need to be erected on surfaces that can support their weight in a stable manner to ensure the safety of the workers and the structure. An adequate firm foundation ensures that the scaffolding remains safe and stable during use. In contrast, using a loose foundation, soft soil, or unstable ground can lead to structural failures, potentially causing accidents and injuries.
For any scaffolding arrangement, always aim for a ground condition or a foundation that is stable, level, and strong enough to bear the load of the scaffold without any risk of subsidence. This may include the use of base plates, sole plates, or a mudsill to distribute the weight and ensure a secure erecting of the scaffolding system.