Which statement is FALSE with respect to the deduction for worthless securities$?$

Question $6$ options:

a$)$

Taxpayers may deduct the cost or other basis of corporate stock in the year that it becomes completely worthless.

b$)$

Taxpayers may take a partial deduction for worthless stock.

c$)$

Securities $($stocks$,$ bonds, debentures, etc.$)$ that become worthless are treated as having been sold or exchanged on the last day of the tax year in which the worthlessness occurs.

d$)$

A taxpayer who is claiming a loss deduction for worthless securities must generally prove that the securities had some value at the end of the preceding tax year or at the beginning of the tax year in which the loss is claimed.