In Order for a Binomial Tree to Recombine,the Following Condition $\mathcal { U }$

In order for a binomial tree to recombine,the following condition is necessary and sufficient:

A) The time-step in the tree must remain constant over time.
B) The up shift factor $\mathcal { U }$
And down shift factor
$d$
Must be such that
$u \times d = 1$
)
C) The up shift factor $\mathcal { U }$
And down shift factor
$d$
Must be such that
$u \times d =$
A constant.
D) The rate of interest must be zero.