What is the difference between a globular cluster and an open cluster?

a
Globular clusters have millions of young stars, tightly bound together where open clusters have thousands of old stars loosely clustered and disorganized.
b
Globular clusters have millions of young stars, loosely clustered and disorganized together where open clusters have thousands of old stars tightly bound together.
c
Globular clusters have millions of old stars, tightly bound together where open clusters have thousands of young stars loosely clustered and disorganized.
d
Globular clusters have millions of old stars, loosely clustered and disorganized together where open clusters have thousands of young stars tightly bound together.