Harry, Ron and Hermione, while hiding, try to decipher the clues left to them by Dumbledore and to destroy Voldemort's Horcruxes after he had took over the Ministry of Magic.
A) Harry, Ron and Hermione, while hiding, try to decipher the clues left by Dumbledore
to them and to destroy Voldemort's Horcruxes after
he had took over the Ministry of Magic.
'to them' is redundant..; also, 'had took' is incorrect grammatically (past participle to be used) B)
Harry, Ron and Hermione, in hiding,
try to decipher the clues left to them by Dumbledore and
to destroy Voldemort's Horcruxes after he takes over the Ministry of Magic.
correct S-V agreement; also, correct parallelismC)
Harry, Ron and Hermione, while in hiding,
tries to decipher the clues left to them by Dumbledore and destroy Voldemort's Horcruxes after he took over the Ministry of Magic.
S-V agreement errorD) Harry, Ron and Hermione, while in hiding, try
to decipher the clues left by Dumbledore to them
and destroy Voldemort's Horcruxes after he takes over the Ministry of Magic.
parallelism errorE) Harry, Ron and Hermione, while in hiding, tried to decipher the clues left to them by Dumbledore and to destroy Voldemort's Horcruxes
after which he took over the Ministry of Magic.
incorrect meaning..antecedent for 'he' is not clear(B) is the correct answer