1. As long as you keep working at it, you will be successful in the end.2. As long as you persevere, you will succeed in the end.3. Ever since he retired, he has been exercising regularly to keep himself in shape.
 keep working at it persevere do something regularly or religiously or consistently or constantlyregularly, religiously, consistently, constantly 都有持之以恆的意思。持之以恆，必定開花結果 = As long as you persevere, you will succeed in the end. = As long as you keep working at it, you will be successful in the end.
Many people in third world countries are living in unsanitay conditions.