In the following diagram showing five parallel signaling pathways downstream of a receptor tyrosine kinase (RTK) and a G-protein-coupled receptor (GPCR), indicate which boxes (A to E) correspond to the following proteins. Your answer would be a five-letter string composed of letters A to E only, e.g. CDBAE. ( ) Cyclic AMP ( ) Protein kinase C ( ) Sos ( ) PI(3,4,5)P3 ( ) Ca2+