The term 'morbidity' refers to:

Correct Answer: B

Rationale: Morbidity (B) is disease frequency or burden (e.g., illness rates). A is mortality, C is incidence, D is population at risk.

Correct Answer: A

Rationale: Secondary attack rate (A) measures infection among contacts of a primary case (e.g., household spread). B, C, and D are broader or vague.

Correct Answer: B

Rationale: Cross-sectional studies (B) measure prevalence at one time (e.g., obesity rates). A requires time, C and D need longitudinal data.

Correct Answer: B

Rationale: Descriptive studies (B) collect quantitative data (e.g., case counts) to describe patterns. A is qualitative, C is experimental, D is broad.

Correct Answer: B

Rationale: Observational studies (B) watch natural events (e.g., smoking-disease links). A and D are experimental, C is a byproduct.