头盔用上四年后，最好更换，因为这时头盔会损耗及老化，无法保证在意外时，能充分发挥保护作用。
It is recommended that you replace a helmet after four years use, as it becomes weathered and aged in that time, and cannot guarantee full protection in a crash.
头盔用上四年后，最好更换，因为这时头盔会损耗及老化，无法保证在意外时，能充分发挥保护作用。
It is recommended that you replace a helmet after four years use, as it becomes weathered and aged in that time, and cannot guarantee full protection in a crash.
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