Explanation:

DNA barcoding is the identification of a species by the characteristic sequence of a standard short section of DNA in its genome. DNA barcoding is done by comparing an individual DNA sequence with a reference library of such DNA sections (called sequences). The introduction of DNA barcoding represents a promising approach for food authentication, being broadly applied in fish species. DNA barcoding has been successful when applied to seafood because the number of species is high in comparison to other animal sources, such as cattle, sheep, goat, and horse, enhancing the effectiveness of the approach. DNA barcoding techniques were used to explore the composition of roasted barley tea (Hordeum vulgare), which was exported to a certain country from China but then returned, due to the detection of other undesirable plant components present. Contaminants were found. Hence option 3 is correct. DNA barcoding will allow users to efficiently recognize known species and speed the discovery of species yet to be found in nature. There have been reports of DNA barcodes used in distinguishing species of tropical Lepidoptera (an order of insects that includes butterflies and moths which are similar). DNA barcodes effectively distinguish among species in three Lepidoptera families from Area de Conservación Guanacaste in northwestern Costa Rica.

Hence option 2 is correct

However, DNA barcoding is not known to be used for the assessment of age of living organisms. Hence option 1 is not correct. Hence (d) is the correct answer.