Hi, there! A1. "可是" and "当然" are two high-frequency vocabulary in Chinese, but we don't put them together when we talk, like "可是当然". "可是" means "but" as you know, and "当然" usually means "of course" OR "but of course". "but of course" here is more closer to "不过". It means something I ***(not)***, but I *** other thing instead. e.g. 虽然上个星期我不能锻炼，可是当然我努力吃健康饮食了。 虽然上个星期我不能锻炼，不过我努力的健康饮食了。 A2.You want to express the movement of "getting down the stairs". So, "走下楼梯" is OK here, but too formal. We usually use "下楼梯" for short when we talk. e.g.我几乎走不动，甚至走下楼梯很痛。 我几乎走不动，甚至下楼梯都很疼