Given below are two statements, one is labelled asAssertion (A) :and other as Reason (R):Assertion (A):Teesta river was earlier a tributary of Ganga, now it is a tributary of Brahmaputra.Reason (R):River capturing is a major feature of Himalayan rivers.Select the correct answer using the codes given below.

1. A

   Both (A) and (R) are true and (R) is the correct explanation of (A).

   Both (A) and (R) are true and (R) is the correct explanation of (A). Assertion (A) records that the Teesta, once linked with the Ganga system, now joins the Brahmaputra system. Reason (R) states that river capturing is a major feature of Himalayan rivers, which is a standard geomorphic process in the young, steep Himalayan drainage. Capture of an older Ganga-bound course by a Brahmaputra-bound head explains the Teesta’s present alignment, so (R) correctly explains (A). This is the official key.

2. B

   Both (A) and (R) are true, but (R) is not the correct explanation of (A).

   Both true but (R) not the correct explanation would apply if Teesta’s shift had some other cause unrelated to capture. Himalayan river capture is precisely the process invoked for this change of master stream. This option is therefore not the key.

3. C

   (A) is true, but (R) is false.

   (A) true and (R) false would require denying river capture in the Himalaya. Capture, piracy of headwaters and elbow of capture are well-recognised Himalayan drainage features. (R) is not false, so this option fails.

4. D

   (A) is false, but (R) is true.

   (A) false and (R) true would deny the Teesta’s change of affiliation. The assertion as framed in the paper is treated as true; the river now belongs to the Brahmaputra system. This option is not the key.

Summary. Official key is (a) Both (A) and (R) are true and (R) is the correct explanation of (A). The Teesta today is a major tributary in the Brahmaputra system after leaving an older Ganga connection. River capture is characteristic of Himalayan rivers because of steep gradients, tectonic uplift and headward erosion. That process accounts for the change stated in (A). Options that split truth or deny the causal link are therefore wrong.