One of the limitations of the case study is that

AThere are very few subjects for which it can ever be applied

BThere are no control groups ✓ Correct

CIt requires a large and expensive sample size

DIt cannot be included in the triangulation method

Correct answer: (B) There are no control groups

Explanation

A key limitation of the case study is that it has no control groups for comparison.

The claim that it applies to very few subjects misstates its scope, as many phenomena suit it.

The idea that it needs a large and expensive sample is wrong, since it studies a single unit intensively.

The claim that it cannot join triangulation is false, as case studies often feed into triangulated designs.

Without a control group, the case study cannot rule out alternative causes of what it observes.

Its strength is depth and rich context, traded against weak generalisability.

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