**Core Concept**
Glomerular filtration and renal reabsorption are two critical processes in the kidney's role of regulating the body's internal environment. Glomerular filtration involves the passage of water and solutes from the blood into the nephron's Bowman's capsule, while reabsorption occurs in the renal tubules, where substances are reabsorbed back into the bloodstream.

**Why the Correct Answer is Right**
Substances that undergo both filtration and reabsorption include glucose, amino acids, and ions such as sodium and potassium. The reabsorption process is highly regulated and involves specific transport mechanisms, such as facilitated diffusion, cotransport, and countertransport. In the case of glucose, it is reabsorbed in the proximal convoluted tubule via a sodium-glucose cotransporter (SGLT2), which helps maintain normal blood glucose levels.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because substances that are completely reabsorbed, such as glucose, are not filtered in the first place.
* **Option B:** This is incorrect because substances that are completely secreted, such as penicillin, do not undergo reabsorption in the renal tubules.
* **Option C:** This is incorrect because substances that are neither filtered nor reabsorbed, such as myoglobin, are not handled by the kidneys in this manner.

**Clinical Pearl / High-Yield Fact**
The kidneys reabsorb approximately 99% of glucose back into the bloodstream, highlighting the importance of the renal tubules in maintaining normal blood glucose levels.

**Correct Answer: D. Glucose**