In a chemical reaction where substance A transfers electrons to substance B, substance A is losing electrons, which means it is being oxidized. Consequently, substance A acts as the reducing agent because it causes the reduction of substance B by donating electrons to it.
Therefore, the correct statement is:
Substance A is oxidized and acts as the reducing agent.
If this option is provided in the responses, please select that one. Otherwise, the closest correct interpretation based on the options would be to clarify any language differences in the options given.