Final answer:
The vicious cycle of malnutrition is best described by malnutrition leading to infection, which then worsens the malnutrition and increases vulnerability to further infections.
Step-by-step explanation:
The sequence that BEST describes the vicious cycle of malnutrition is a) Malnutrition, infection, worsening malnutrition, increased vulnerability to infection. This cycle demonstrates the interplay between undernutrition and infectious disease. Children suffering from malnutrition have weakened immune systems, rendering them more susceptible to infections. In turn, infectious diseases can exacerbate malnutrition due to increased nutritional needs and reduced nutrient absorption caused by symptoms like vomiting and diarrhea. Therefore, malnutrition and infections reinforce each other, creating a synergistic relationship that can lead to a downward spiral of worsening health.