Difficulty: Easy
Correct Answer: Only conclusion I follows.
Explanation:
Given data
Concept / Approach
 Use set relations: If some Actors ∩ Singers ≠ ∅ and Singers ⊆ Dancers, then those same actors are also Dancers. A universal negative about singers vs actors contradicts S1.
Step-by-step check
 From S1: ∃x such that x ∈ Actors and x ∈ Singers. From S2: Singers ⊆ Dancers ⇒ Any singer is a dancer. Therefore that x is also a Dancer ⇒ Some actors are dancers ⇒ C1 is true. C2 says “No singer is actor,” which directly contradicts S1 ⇒ C2 is false. 
Common pitfalls
 Assuming “some” means “all,” or overlooking subset propagation (Singers ⊆ Dancers). 
Final Answer
 Only conclusion I follows. 
Discussion & Comments