A subcontractor begins work on a private project on March 1. To preserve lien rights, the preliminary notice must be served by:

Explanation

Civil Code §8200 requires the preliminary notice to be served not later than 20 days after the claimant first furnishes labor, service, equipment, or materials, so work starting March 1 puts the deadline at March 21. (a) treats the notice as a condition of starting work; it is not, and a notice served on day one is valid but early. (b) borrows a ten-day period that appears elsewhere in construction practice, not here. (c) rounds to a month. Late service does not destroy the lien outright: under §8204 it limits the claim to work furnished in the 20 days before service and afterwards.