Among five friends A, B, C, D and E, who is the tallest? Statement I: D is taller than A and C. Statement II: B is shorter than E but taller than D.

Introduction / Context:
This data sufficiency problem concerns comparative heights among five friends. The question asks you to identify the tallest person among A, B, C, D, and E. Two statements describe relative height relationships. The challenge is to see whether either statement alone, or both together, provide enough information to determine who is tallest in the group.

Given Data / Assumptions:
- The friends are A, B, C, D and E.
- Question: Who is the tallest among them?
- Statement I: D is taller than A and C.
- Statement II: B is shorter than E but taller than D.
- No one else beyond A, B, C, D and E is being considered when we say "tallest".

Concept / Approach:
To solve ordering problems like this, we build partial orders of individuals based on given comparisons. We start with one statement, derive as much ordering as possible, then do the same for the second statement. If neither statement alone yields a complete picture, we combine the information from both to see whether we can now identify a unique tallest person. The key is to keep track of all inequalities and see whether any person is known to be taller than all others.

Step-by-Step Solution:
Step 1: Use statement I alone. It tells us D is taller than A and C, so D > A and D > C. We still know nothing about B and E relative to D, A, or C. Therefore, we cannot decide who is tallest among all five friends. Statement I alone is not sufficient. Step 2: Use statement II alone. It states that B is shorter than E but taller than D, so E > B > D. However, we still know nothing about where A and C stand in comparison to E or B. So, statement II alone is also not sufficient. Step 3: Combine both statements. From statement I we have D > A and D > C. From statement II we have E > B > D. Step 4: Joining these, we get a chain: E > B > D > A and D > C. That means E is taller than B, D, A, and C. There is no information about anyone taller than E. Step 5: Therefore E is taller than every other friend in the group. So E is the tallest.

Verification / Alternative check:
We can quickly test whether any other person could possibly be tallest while still satisfying the statements. A or C cannot be taller, because statement I explicitly says that D is taller than both A and C, and statement II says B is taller than D, and E is taller than B. That already places A and C strictly below D, B and E. B cannot be tallest because E is stated to be taller than B. D cannot be tallest because B is taller than D. Thus E is the only candidate left, and the conclusion is unique.

Why Other Options Are Wrong:
- Option a is wrong because statement I alone leaves B and E completely unranked relative to D, A, and C, so we cannot find the tallest.
- Option b is wrong because statement II alone does not locate A and C in the order, again preventing a unique answer.
- Option c is incorrect because neither statement by itself is sufficient; both are required together.
- Option e is wrong because we have shown that both statements combined clearly identify E as the tallest friend.

Common Pitfalls:
Some students prematurely conclude that E is tallest using statement II alone, forgetting that A or C might still be taller in the absence of more information. Others do not fully integrate the inequalities when combining the statements and therefore underestimate what can be concluded. Always write down or mentally picture the complete order implied by each statement and then merge them systematically.

Final Answer:
Only when both statements are used together can we conclude that E is the tallest among the five friends. Thus, the correct data sufficiency choice is option D.