Question

3. I've been working for over twenty years and seldom        as now. (tired)

我已经工作二十多年了，很少感觉像现在这样累过。

Answer 1

3. have I felt so tired否定副词seldom位于句首时(第二个分句的句首) ，句子应用部分倒装结构;根据句意，应用现在完成时态。