回複：延一次三年，特殊情況再給延一年。

You can 延 n 次, subject to 6 years limit.
If LC/I-140 pending for over 365 days, you can extend one year at a time, also no limit how many times you can extend after 6-year, as long as LC/I-140 pending (very clear by law) or I-140 approved and waiting for I-485 (law is not clear, but some people succeeded).