I, J, K and L are distinct individuals. I is the daughter of J. J is the son of K, and K is the father of L. B is the son of J, and B has one brother D. Based on these family relations, which of the following statements are true: I. I is the sister of D. II. D and B are brothers. III. K is the grandfather of D?

Introduction / Context:
This reasoning problem introduces several people, I, J, K, L, B and D, and describes how they are connected as parents and children. We are given three statements about their relationships and asked to decide which ones are true. Such questions require building a clear mental or written family tree and then carefully checking each statement against that structure.

Given Data / Assumptions:
• I is the daughter of J, so I is a child of J and female.• J is the son of K, so J is a child of K and male.• K is the father of L, so L is another child of K.• B is the son of J, so B is a child of J and male.• B has one brother, D, so D is also a son of J.• Therefore J has at least three children: I, B and D.

Concept / Approach:
Once we recognise J as the parent of I, B and D, and K as the parent of J, it becomes easy to evaluate the proposed statements. Statement I says that I is the sister of D, which matches the data because I and D share the same father J and I is female. Statement II says that D and B are brothers, which matches because both are male children of J. Statement III says that K is the grandfather of D, which is correct as K is the father of J and J is the father of D. All three statements are therefore true.

Step-by-Step Solution:
Step 1: From I is the daughter of J, mark I as female child of J.Step 2: From B is the son of J and B has one brother D, mark B and D as male children of J.Step 3: Conclude that J is parent of I, B and D.Step 4: From J is the son of K, note that K is one generation above J, thus grandparent to I, B and D.Step 5: Check statement I: I and D share parent J and I is female, so I is sister of D. This is true.Step 6: Check statement II: D and B are both sons of J, which confirms they are brothers. This is true.Step 7: Check statement III: K is father of J and J is father of D, hence K is grandfather of D. This is also true.

Verification / Alternative check:
A quick family tree has K at the top, with children J and L on the next line. J then has three children: I (daughter), B (son) and D (son). From this diagram, we can visually see that I is sister to B and D, B and D are brothers to each other, and K is grandparent to all three. There is no way to interpret the data so that any of the statements becomes false without contradicting the given information.

Why Other Options Are Wrong:
Only statement I is true: This ignores the clearly correct relations in statements II and III.Statements I and II are true: This wrongly discards statement III, even though K is explicitly the father of J, who is father of D.Only statement III is true: This would ignore the direct sibling relations among I, B and D.None of the statements is true: This is clearly inconsistent with the given family structure.

Common Pitfalls:
Sometimes candidates forget that B having one brother D does not exclude other sisters, so they do not realise I is also a child of J. Others only track one or two links and therefore fail to see the grandparent relationship in statement III. Drawing a simple diagram is an excellent way to avoid such mistakes and confirm that all three statements are indeed true.

Final Answer:
All of the statements I, II and III are true.