Statements: • Some birds are goats. • Some goats are horses. • Some horses are lions. • Some lions are tigers. Conclusions: I. Some tigers are goats. II. No tiger is a goat. III. Some lions are birds. IV. No lion is a bird. Choose the option that must follow.

Introduction / Context:
This is a chain of four independent “some” statements. Without any universal inclusion connecting them, none of the extreme overlaps is forced, and neither of the “either … or …” patterns is logically necessary.

Given Data / Assumptions:
Each premise provides a separate intersection: Birds∩Goats, Goats∩Horses, Horses∩Lions, Lions∩Tigers. They may involve entirely different individuals.

Concept / Approach:
To prove I (“Some tigers are goats”) we would need one element to travel through Goats, Horses, Lions into Tigers. The premises do not require that. To prove II (“No tiger is a goat”) we would need a universal exclusion between Tigers and Goats, which we do not have. The same analysis applies to III and IV with Lions and Birds.

Step-by-Step Solution:
• Build Model A where all four intersections are witnessed by different individuals; then I–IV are all false.• Build Model B where the chain coincides for a single individual; then I and III are true, II and IV are false. Because truth values vary with permitted models, none of I–IV is necessary.

Verification / Alternative check:
The “either … or … follows” options are used only when exactly one of a pair must be true. Here, both can be false in Model A, so neither “either … or …” is guaranteed.

Why Other Options Are Wrong:
They assume forced overlap or forced exclusion that is not present.

Common Pitfalls:
Confusing possibility with necessity in chains of “some.”

Final Answer:
None follows.