I disagree with the OA for question 1. According to the stable state's definition and analogy in the passage, it mentions the ability for the ball to roll back into the original valley, indicating that an environment under the stable state should theoretically be able to transition back into its original state, provided the extrinsic push is hard enough for the ball to crossover back to its initial valley.
In option A, there is no conceivable way this can be accomplished. Under what circumstances will permit the stable state ecology to transition back to the original valley? Even if the ex-banker's severe illness is magically cured instantly, does he return back to his initial job?
On the other hand, option D explicitly states that the stock price only returns back when "the rumour is debunked". In this option, the ball travels to the second valley upon news of the takeover bid, followed by a large enough push (which is the debunking of rumours) to bring the ball back to the first valley. If not for the rumours being debunked, it is only fair to assume that the news of the takeover bid is in fact true, and thus justifying the increased stock price. In such a case, the ball will stay in the second valley; the stock price will remain increased.
Would love to hear anyone's explanation if they disagree with regards to my POV of the ability to return to the original state.