Answer: Based on the context, the word 'gained' is used to mean "reach".
Step-by-step explanation: The word 'gained' has several meanings. One of them is to reach or arrive at a specific place or destination. In the sentence provided, the destination is "the top of the startcase", which is part of the context of the sentence, and the word 'gained' has been used to indicate that they arrived at that destination. Therefore, "gained" is used to mean "reach" and not "left behind", "made" or "seen".