White's decisions on the second and third move depends on the way he wants to meet the Queen's Gambit and the Slav/Meran/Chebanenko. Semkov covers in detail the different options, and also devotes several chapters on 1.Nf3 d5 2.e3 Nf6 3.c4 c6 and 3...e6 4.b3! (avoiding the innocuous version of the QGA after 4.Nc3 dxc4). There is another chapter on 1.Nf3 d5 2.e3 Nf6 3.c4 dxc4, where the absence of Nc3 allows White to get some pressure by refraining from d2-d4.