Evolution of disk accretion rate (black) and characteristic disk size (blue). When Ṁ_g < Ṁ_pho (Eq. (6)), the disk angular momentum is transported by viscous accretion; later the gas removal is driven by stellar X-ray evaporation. The expansion of the disk sizes are shown insolid lines due to viscous spreading. Top: three systems with different initial disk sizes (R_d0 = 30 AU, 100 AU and 160 AU) are shown around a 1 M_⊙ star. The initial disk accretion rates are all 6 × 10⁻⁸ M_⊙ yr⁻¹. Bottom: three systems with the same initial disk size (R_d0 = 100 AU) are shown around different masses of stars (M_⋆ = 1 M_⊙, 0.3 M_⊙ and 0.1 M_⊙). The initial disk accretion rates follow . We would like to note that the two panels share the same x-axis.