  The evolution of giant molecular clouds (GMCs), the main sites of high-mass
star formation, is an essential process to unravel the galaxy evolution. Using
a GMC catalogue of M33 from ALMA-ACA survey, we classified 848 GMCs into three
types based on the association with HII regions and their H$\alpha$
luminosities $\textit{L}$(H$\alpha$): Type I is associated with no HII regions;
Type II with HII regions of $\textit{L}$(H$\alpha$) $<$ 10$^{37.5}$ erg
s$^{-1}$; and Type III with HII regions of $\textit{L}$(H$\alpha$) $\geqq$
10$^{37.5}$ erg s$^{-1}$. These criteria yield 224 Type I GMCs, 473 Type II
GMCs, and 151 Type III GMCs. GMCs show changes in their physical properties
according to the types; mass, radius, velocity dispersion, and $^{13}$CO
detection rate of GMCs systematically increase from Type I to Type III, and
additionally, Type III GMCs are closest to virial equilibrium. Type III GMCs
show the highest spatial correlation with clusters younger than 10 Myr, Type II
GMCs moderate correlation, and Type I GMCs are almost uncorrelated. We
interpret that these types indicate an evolutionary sequence from Type I to
Type II, and then to Type III with timescales of 4 Myr, 13 Myr, and 5 Myr,
respectively, indicating the GMC lifetime of 22 Myr by assuming that Type II
GMC has the same timescale as the Large Magellanic Cloud. The evolved GMCs
concentrate on the spiral arms, while the younger GMCs are apart from the arm
both to the leading and trailing sides. This indicated that GMCs collide with
each other by the spiral potential, leading to the compression of GMCs and the
triggering of high-mass star formation, which may support the dynamic spiral
model. Overall, we suggest that the GMC evolution concept helps illuminate the
galaxy evolution, including the spiral arm formation.
