The number of registered participants in this year's marathon was half _________.

A．that of last year's                                         B．those of last year's

C．those of last year.                                       D．of last year's

The number of registered participants in this year’d marathon was half        ．

    A．of last year’s                            B．those of last year’s

    C．that of last year’s                      D．of those of last year