A deductible temporary difference arises when the carrying amount of an asset or liability in the financial statements is higher than its tax base, which will result in a future tax deduction.

A. This situation represents a deductible temporary difference because the expense has been recognized for accounting purposes but will only be deductible for tax purposes when the cash is actually paid, creating a difference in the timing of the expense.

B. This is a taxable temporary difference, as the tax base is lower than the carrying amount for tax purposes.

C. This is not a temporary difference, as there is no difference between the carrying amount for financial reporting and tax purposes; the lack of tax consequences upon collection means there's no tax benefit to be realized in the future.

Therefore, the correct answer is: A. Research expenditure that was accrued in the amount of 50, but will be tax deductible on a cash basis.