The signs and symptoms of large bowel obstruction are:

Choice A reason:
Loss of muscle tone at the lower esophageal sphincter (LES) is the primary cause of GERD. The LES normally prevents stomach contents from refluxing into the esophagus. When its tone is reduced, acidic gastric contents can flow back, leading to symptoms such as heartburn, regurgitation, and potential damage to the esophageal lining. Factors contributing to LES dysfunction include obesity, hiatal hernia, and certain dietary habits.
Choice B reason:
Sympathetic nerve stimulation is not a cause of GERD. The autonomic nervous system plays a role in regulating digestive functions, but GERD is primarily a mechanical issue involving the LES and is not directly related to sympathetic nervous activity.
Choice C reason:
Fibrosis of the lower third of the esophagus is typically associated with conditions such as scleroderma, which can lead to esophageal motility disorders. While fibrosis might contribute to esophageal dysfunction, it is not the primary cause of GERD.
Choice D reason:
Reverse peristalsis of the stomach is not a mechanism for GERD. GERD results from dysfunction of the LES, not from the backward movement of stomach contents due to altered motility.

Choice A reason:
Viruses are known for their unique replication process. They cannot replicate independently and must hijack a host cell's machinery to reproduce. This characteristic is fundamental to understanding viruses and is a key concept in virology. By replicating their genetic material inside host cells, viruses ensure their propagation and survival. This answer is correct because it highlights this crucial aspect of viral biology.
Choice B reason:
This choice is incorrect because viruses are not easily killed by antimicrobials. Antimicrobials, such as antibiotics, are typically effective against bacteria, not viruses. Viruses have different structures and replication mechanisms that make them resistant to these treatments. Instead, antiviral medications are needed to target viruses specifically.
Choice C reason:
This choice is also incorrect. Viruses do contain either DNA or RNA as their genetic material. This genetic material is essential for their replication and propagation. Some viruses have DNA, while others have RNA, and this distinction is one of the primary ways viruses are classified.
Choice D reason:
Viruses are not capable of independent reproduction. They rely entirely on infecting host cells to replicate. This dependence on host cells distinguishes them from other microorganisms like bacteria, which can reproduce on their own. Thus, this choice is incorrect as it does not accurately reflect the nature of viruses.