13 .The factors influencing the circles of sustainability are:Economics and PoliticsEcology and cultureNeither (a) nor (b)Both (a) and (b)

The question is asking about the factors that influence the circles of sustainability. To address this, let's break down the options provided:

1. Economics and Politics: This refers to the financial systems, market dynamics, and political frameworks that shape sustainability. Economic practices and political policies play a critical role in sustainability efforts.

2. Ecology and Culture: This highlights the environmental aspects and cultural values that impact sustainability. Ecological considerations address the health of ecosystems, while cultural factors influence how communities engage with sustainability.

3. Neither (a) nor (b): This option suggests that neither of the previous sets of factors influences sustainability.

4. Both (a) and (b): This option posits that both sets of factors, economics & politics and ecology & culture, jointly influence sustainability.

Analysis

Sustainability is a complex concept influenced by a myriad of factors. From the analysis, it's clear that both economic/political and ecological/cultural elements are essential to understanding and implementing strategies for sustainable development.

Conclusion

The correct option is Both (a) and (b) as both sets of factors play significant roles in the circles of sustainability.

Final Answer

Both (a) and (b).