To solve this problem, we need to understand the impact of deleting a base from an RNA sequence on the codons that follow the deletion.$\newline \bullet$An RNA sequence is read in sets of three bases, known as codons, each of which codes for one amino acid.$\newline \bullet$Given that the RNA has 999 bases, it originally forms $\frac{999}{3} = 333$ codons, corresponding to 333 amino acids.$\newline \bullet$If the base at position 901 is deleted, the sequence will shift, causing a frameshift mutation.$\newline \bullet$This frameshift will affect all codons from position 901 onwards.$\newline \bullet$To determine how many codons are altered, we calculate the number of codons from position 901 to the end of the RNA.$\newline \bullet$The number of bases from position 901 to 999 is $999 - 901 + 1 = 99$ bases.$\newline \bullet$These 99 bases originally form $\frac{99}{3} = 33$ codons.$\newline \bullet$Therefore, 33 codons will be altered due to the deletion.$\newline$Thus, the correct answer is Option 2: 33.