Internal structure of KIC 9145955, KIC 9970396, KIC 9882316, and KIC 11968334. The vertical red dashed lines in panels (a)–(d) denote the helium core boundary where the hydrogen mass fraction is about 0.01. The vertical orange dashed lines in panels (a)–(d) denote the base of the convection zone, which is marked as q_bcz. The blue crosses in panels (a)–(d) represent the reaction rate of the carbon, nitrogen, and oxygen (CNO) cycle.