The type of volcano with broad and gentle slopes built by the eruption of fluid basalt lava is called a shield volcano.

Here's why:

* Fluid Basalt Lava: Basalt lava is very fluid, meaning it flows easily and spreads out over a wide area. This creates the characteristic broad, gently sloping shape of shield volcanoes.

* Gentle Slopes: Because the lava flows easily, it doesn't build up steep, cone-shaped structures like other types of volcanoes.

* Large Size: Shield volcanoes are often very large, with diameters that can stretch for miles. This is due to the vast amount of lava that erupts over time.

Examples of shield volcanoes:

* Mauna Loa (Hawaii): The largest active volcano on Earth.

* Kilauea (Hawaii): Another famous shield volcano in Hawaii, known for its frequent eruptions.

Let me know if you have any other questions!