Explanation:

The correct answer is option 'D', which states that the genetic code is triplet. Let's understand why this is the correct answer in detail.

Genetic Code:
- The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences).
- The genetic code consists of sequences of three nucleotides called codons, which specify the amino acids that will be incorporated into a protein during translation.
- Each codon codes for a specific amino acid or a stop signal.

Codons and Amino Acids:
- There are a total of 64 possible codons (4 nucleotides in DNA/RNA combined in sets of 3).
- Out of these 64 codons, 61 code for amino acids and 3 serve as stop signals to terminate protein synthesis.
- Hence, there are 61 sense codons and 3 nonsense (stop) codons.

Nonsense and Sense Codons:
- Nonsense codons, also known as stop codons, signal the termination of protein synthesis. They are UAA, UAG, and UGA.
- Sense codons, also known as coding codons, specify the amino acids that will be incorporated into a protein. There are 61 sense codons that code for the 20 different amino acids.

Triplet Code:
- The genetic code is triplet, meaning that each codon consists of three nucleotides.
- This triplet code allows for the generation of a large number of different codons (4^3 = 64), providing enough variation to encode all the required amino acids and stop signals.

Other Options:
- Option 'A' is incorrect because the number of codons (64) is greater than the number of amino acids (20), which means that multiple codons can code for the same amino acid.
- Option 'B' is incorrect because although there are 64 types of tRNAs (one for each codon), this is not the reason for the number of codons being 64.
- Option 'C' is incorrect because it states that there are 44 nonsense codons and 20 sense codons, which is not accurate. There are 61 sense codons and 3 nonsense codons.

Conclusion:
In summary, the correct answer is option 'D' because the genetic code is indeed triplet, meaning that each codon consists of three nucleotides. This triplet code allows for the encoding of 61 sense codons (amino acids) and 3 nonsense codons (stop signals) out of the total 64 codons.