Final answer:
Very fluid lava contributes to the gentle slopes characteristic of shield volcanoes.
Step-by-step explanation:
The factor that contributes to the gentle slopes characteristic of shield volcanoes is very fluid lava. Unlike other types of volcanoes, shield volcanoes are formed by eruptions of runny lava, which flows easily and spreads out in thin layers. This lava has low viscosity, meaning it is not very sticky and can flow quickly and smoothly.
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