  Herein, we present results from observations of the 12CO (J=1-0), 13CO
(J=1-0), and 12CO (J=2-1) emission lines toward the Carina nebula complex (CNC)
obtained with the Mopra and NANTEN2 telescopes. We focused on
massive-star-forming regions associated with the CNC including the three star
clusters Tr14, Tr15, and Tr16, and the isolated WR-star HD92740. We found that
the molecular clouds in the CNC are separated into mainly four clouds at
velocities -27, -20, -14, and -8 km/s. Their masses are 0.7x10^4Msun, 5.0x10^4
Msun, 1.6x10^4 Msun, and 0.7x10^4 Msun, respectively. Most are likely
associated with the star clusters, because of their high 12CO (J=2-1)/12CO
(J=1-0) intensity ratios and their correspondence to the Spitzer 8 micron
distributions. In addition, these clouds show the observational signatures of
cloud--cloud collisions. In particular, there is a V-shaped structure in the
position--velocity diagram and a complementary spatial distribution between the
-20 km/s cloud and the -14 km/s cloud. Based on these observational signatures,
we propose a scenario wherein the formation of massive stars in the clusters
was triggered by a collision between the two clouds. By using the path length
of the collision and the assumed velocity separation, we estimate the timescale
of the collision to be ~1 Myr. This is comparable to the ages of the clusters
estimated in previous studies.
