The control of gene A is only at the translational level if:
Regulation solely at translational level implies mRNA abundance remains constant while protein output changes due to post-transcriptional mechanisms. If gene A is controlled translationally, quantitative RT-PCR or Northern blot shows unchanged transcript levels across experimental conditions, whereas Western blot reveals increased protein due to enhanced ribosome recruitment, cap-dependent initiation, relief of upstream open reading frames or loss of microRNA repression at untranslated regions. Parallel rise in RNA and protein would indicate transcriptional control, while decreasing RNA suggests decay or repression rather than exclusive translational regulation.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.