Arrange these events of mitosis in their correct sequence:
$a -$ Nuclear envelope assembles around chromosome clusters.
$b -$ Spindle fibers attach to kinetochores of chromosomes.
$c -$ Condensation of chromosomes.
$d -$ Centromeres split and chromatids separate.

• A
  $b \rightarrow c \rightarrow a \rightarrow d$
• B
  $a \rightarrow b \rightarrow d \rightarrow c$
• C
  $c \rightarrow d \rightarrow b \rightarrow a$
• D
  $c \rightarrow b \rightarrow d \rightarrow a$