[求助]xdf 语法网络课堂一题求助

7. The most common reasons for an
employee's unwillingness to accept a transfer are that    mortgage rates are high, housing in the
new location costs more, and the difficulty of selling
            the old home.

    (A)
that mortgage rates are high, housing in the new location costs more, and the
difficulty of       selling the old home.

    (B)
that mortgage rates are high, housing in the new location costs more, and that
it is    difficult to sell the old home

    (C)
high mortgage rates, the greater cost of housing in the new location, and that
the old       home is difficult to sell

    (D)
high mortgage rates, the greater cost of housing in the new location, and it is
difficult to
            sell the old home

    (E) high mortgage rates, the greater cost of
housing in the new location, and the difficulty of        selling the old home

最近刚准备考gmat,在听赵丽的语法讲座，有一题实在不解，不知为何选d而不选e,请高手指教。