A method for obtaining urea prills in a prilling tower comprising the step of making a plurality of melt urea droplets to fall from a urea melt distributing device towards an urea prills collecting bottom of the prilling tower, further comprises the step of cooling the collecting bottom. The gate structure of the elementary cell includes a first conductor material finger. And the shower apparatus uses an illuminating device to obtain a relaxing atmosphere. If the written sequence of numbers of the protected register matches a reference sequence of numbers, a rewrite circuit is configured to write the second portion of the protected register. The gas introduction system comprises a gas introduction conduit and a bypass conduit. Thus, the seat assembly can adjust its width to meet individual body dimension of rider.