3. When I retire I'll participate in programs to keep mentally active.
退休后，我要参加一个终身学习项目来保持思想的青春活力。
4. To keep up with the changing world, one must be involved in lifelong learning and be ready to accept new things.
在这个瞬息万变的信息时代，要赶上社会发展的步伐，终生学习已成为当务之急，必须做好准备，接受新事物。