Is it a Subset?

Discrete Mathematics Level 1

$$A = \{6,2,4,1,5\}$$.

Which of the options below is not a proper subset of $$A$$?

• $$\{2\}$$
• $$\{1,2,3\}$$
• $$\{6,5,2,1\}$$
• $$\{1,2,4,5\}$$
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