6. What is \( \# 4 \) ? (Underneath layer \( \# 3 \) ) \( \begin{array}{ll}\text { A) Lithosphere } & \text { C) Asthenosphere } \\ \text { B) Crust } & \text { D) Mantle }\end{array} \)

To determine what \( \# 4 \) is underneath layer \( \# 3 \), we need to understand the typical structure of the Earth's layers. 1. The outermost layer is the **Crust** (often referred to as layer \( \# 1 \)). 2. Below the crust is the **Mantle** (layer \( \# 2 \)). 3. The **Asthenosphere** is a part of the upper mantle, which is often considered as layer \( \# 3 \) in some models. If we consider the layers in a typical geological model, the layer directly beneath the Asthenosphere (layer \( \# 3 \)) would be the **Lithosphere** (which includes the crust and the uppermost part of the mantle). Given the options: - A) Lithosphere - B) Crust - C) Asthenosphere - D) Mantle The correct answer for \( \# 4 \) (the layer underneath layer \( \# 3 \), which is the Asthenosphere) would be: **D) Mantle**.