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Consider the following statements :

(a) Every non-empty open subset of R is uncountable.
(b) Every connected subset of R containing at least two elements is uncountable.

Then :

  • A.Only (a) is true
  • B.Only (b) is true
  • C.Both (a) and (b) are true
  • D.Both (a) and (b) are false

Answer: C

Both (a) and (b) are true.

(a) A non-empty open subset of R contains an open interval \((x - \varepsilon, x + \varepsilon)\), and every non-degenerate interval is uncountable, so the set is uncountable.

(b) The connected subsets of R are exactly the intervals. A connected set containing two points \(a \lt b\) therefore contains the whole interval \([a, b]\), which is uncountable.

Since both statements hold, the options saying only one is true, or both false, are wrong.

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