  Stellar rotation, age spread and binary stars are thought to be three most
possible causes of the peculiar color-magnitude diagrams (CMDs) of some star
clusters, which exhibit extended main-sequence turn-offs (eMSTOs). It is far
from getting a clear answer. This paper studies the effects of three above
causes on the CMDs of star clusters systematically. A rapid stellar
evolutionary code and a recently published database of rotational effects of
single stars have been used, via an advanced stellar population synthesis
technique. As a result, we find a consistent result for rotation to recent
works, which suggests that rotation is able to explain, at least partially, the
eMSTOs of clusters, if clusters are not too old ($<$ 2.0\,Gyr). In addition, an
age spread of 200 to 500\,Myr reproduces extended turn-offs for all clusters
younger than 2.5\,Gyr, in particular, for those younger than 2.2\,Gyr. Age
spread also results in extended red clumps (eRCs) for clusters younger than
0.5\,Gyr. The younger the clusters, the clearer the eRC structures. Moreover,
it is shown that binaries (including interactive binaries) affect the spread of
MSTO slightly for old clusters, but they can contribute to the eMSTOs of
clusters younger than 0.5\,Gyr. Our result suggests a possible way to
disentangle the roles of stellar rotation and age spread, i.e., checking the
existence of CMDs with both eMSTO and eRC in clusters younger than 0.5\,Gyr.
