The correct answer is A. Debited.
In a journal entry, the left side is called the debit side and the right side is called the credit side. Debits increase asset accounts and decrease liability and equity accounts. Credits increase liability and equity accounts and decrease asset accounts.
In the case of machinery purchased, the machinery account is an asset account. Therefore, the machinery account will be debited.
The other options are incorrect. Option B is incorrect because a credit would decrease the machinery account. Option C is incorrect because both the debit and credit sides of the journal entry would not be affected. Option D is incorrect because the machinery account is an asset account and asset accounts are debited when they are increased.