Select the option that will improve the underlined part of the given sentence. In case no improvement is needed, select 'No improvement required'.

Although the waters may have receded, the aftermath of one of the world's biggest natural disaster had only just begun.

A

the aftermath of one of the world's biggest natural disasters

B

No improvement required

C

the aftermath of one of the worlds' biggest natural disasters has

D

the aftermath of one of the worlds' biggest natural disaster