**Core Concept**
A dideoxynucleotide is a type of nucleotide used in DNA sequencing, lacking hydroxyl groups at both the 2' and 3' positions of the sugar moiety. This modification prevents further extension of the DNA strand. Dideoxynucleotides are also known as chain terminators.

**Why the Correct Answer is Right**
The correct answer is related to the structure of dideoxynucleotides. Since they are used as chain terminators in DNA sequencing, their structure must prevent the formation of a phosphodiester bond between the 3' carbon of the sugar and the next incoming nucleotide. This is achieved by the absence of a hydroxyl group at the 3' position.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might seem plausible but is incorrect because the absence of a hydroxyl group at the 2' position is indeed a characteristic of dideoxynucleotides.
**Option B:** This is also incorrect as dideoxynucleotides do contain a phosphate group, which is necessary for their incorporation into the DNA strand.
**Option C:** This option is the correct answer but for the sake of explanation, if we consider an incorrect option related to the sugar moiety, it would be incorrect because dideoxynucleotides do contain a sugar moiety, albeit modified.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** Cannot be evaluated as the options are not provided.

**Clinical Pearl / High-Yield Fact**
Dideoxynucleotides are crucial in the Sanger sequencing method, allowing for the determination of the order of nucleotides in DNA. Their role as chain terminators is fundamental to this process.

**Correct Answer:** D. hydroxyl groups at both the 2' and 3' positions