How does talin activate the inside-out signaling through integrin?

A) It binds to both integrin subunits to bring them together in an interlocked conformation.
B) It is a protein kinase that phosphorylates both integrin subunits and induces activation by conformational change.
C) It competes with the α subunit for binding to the β subunit, therefore blocking intimate α-β linkage.
D) It binds to the α subunit, and dissociates the dimer into individual subunits that are functionally active.