Three statements are given, followed by four conclusions numbered I, II, III and IV. Assuming the statements to be true, even if they seem to be at variance with commonly known facts, decide which of the conclusions logically follow(s) from the statements?
Statements :
1. All boats are fishes.
2. Some fishes are rivers.
3. Some rivers are sailors.
Conclusions :
I. Some sailors are fishes.
II. Some boats are sailors.
III. Some rivers are boats.
IV. Some fishes are boats.

Given:

Statements :
1. All boats are fishes.
2. Some fishes are rivers.
3. Some rivers are sailors.
From the above following Venn diagram will be - 

From the above Venn diagram - 

We know: Some rivers are sailors, and some fishes are rivers. However, there is no guaranteed direct link between the same “some” rivers. The overlapping parts may or may not be the same. Not definitely true.

All boats are fishes, but there is no direct or indirect link connecting boats to sailors. False / Not definitely true.

All boats are fishes, and some fishes are rivers, but that doesn’t necessarily mean those “some fishes” are boats. Not definitely true.

Conclusion IV: Some fishes are boats. All boats are fishes, so it is logically true that some fishes are boats (since boats are a subset of fishes). Definitely true.

Correct answer is (D) Only conclusion IV follows.