Which of the following might have contributed to greater biological diversity in tropics?
(a) Frequent glaciations in the past 
(b) More constant environments that promote niche specialisation
(c) More solar energy availability contributing to more productivity

Tropics have greater biodiversity compared to temperate regions because

• Speciation is generally a function of time, temperate regions are subjected to glaciations more frequently than the tropics. The tropics ae much more stable and have been undisturbed for years, and hence, have more species diversity.
• Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
• There is more solar energy available in the tropics, which contributes to higher productivity; this in turn may contribute indirectly to greater diversity.