"A good statesman, like any other sensible human being, learns more from his opponents than from his fervent supporters. For his supporters will push him to disaster unless his opponents show him where the dangers are. So if he is wise he will often pray to be delivered from his friends, because they will ruin him. But, though it hurts, he ought also to pray never to be left without opponents; for they keep him on the path of reason and good sense. The national unity of free people depends upon a sufficiently even balance of political power to make it impracticable for the administration to be arbitrary and for opposition to be revolutionary and irreconcilable."

What is $\mathbf{X}$ in the sequence $1,3,6,11,18, X, 42$ ?

Consider the sequence:

A_BCD_BBCDABC_DABC_D

that follows a certain pattern. Which one of the following completes the sequence?

What is the middle term of the sequence

Z, Z, Y, Y, Y, X, X, X, X, W, W, W, W, W ____, A?

Replace the incorrect term by the correct term in the given sequence

3, 2, 7, 4, 13, 10, 21, 18, 31, 28, 43, 40

where odd terms and even terms follow the same pattern.