First 3-4 subtasks are possible with brute force only, right?

Would you please explain me why answer is always subarray of length 1 or 2?

And would You please define a notion of subarray?, is it a continuous segment in array?

fact: depth[lca(a, b)] >= depth[lca(a, b, c)]

Let's denote V as set of vertices which are in subtree(v), so if we'll increase size of V, lca of all vertices of V won't at least become more distant from v, so all we need to do is find two vertices(x, y), lca(x, y) = v & if we'll denote i as index of x and j as index of y in array, is it correct that all vertices in range[i, j] in array must be in subtree(v) to say that answer for current query is (x, y)?

Thanks in advance!

UPD: I forgot that fact that those vertices (x, y) must be in two different children of vertex v, how should I do there?

UPD': Probably, I got it! Thank you very much! But here's last request to confirm something: if we have set of vertices V that all vertices locate in subtree of v, will it be correct & enough to consider always & only adjacent vertices from set V?