The Pre-B-Cell Receptor Provides an Important Signal That Induces Transition $\lambda$

The pre-B-cell receptor provides an important signal that induces transition of pro-B cells to pre-B cells. An important characteristic of this receptor is that:

A) It signals without binding to an extracellular ligand.
B) It is composed of immunoglobulin heavy chains and the VJ region of a rearranged $\lambda$ light chain.
C) It is expressed at very high levels on the surface of the pro-B cell.
D) It signals without requiring association with B-cell receptor signaling subunits, Ig $\alpha$ and Ig $\beta$ .
E) It signals without requiring the B-cell receptor signaling kinase, BTK.