A hearing enhancement communication link within which a hearing aid speaker is connected, whereby to supply loud and clear audio messages over a full range of frequencies from a receivertransmitter directly to the ear of the user in order to overcome the adverse effects of loud background noises andor a hearing impairment of the user. The method includes: closing the recirculation valve and a fill valve in a supply line that supplies LNG; monitoring a mass of the LNG flowing through the recirculation line to ensure that the mass flowing therethrough is less than an acceptable threshold; and aborting any pending sales if the mass of the LNG flowing therethrough is not less than the acceptable threshold. Thus, the substrate cleaning apparatus can be provided which is capable of reducing an operation time required for removing foreign matters, enhancing operation efficiency, stably and reliably removing foreign matters, and restraining operation time even if the size of the substrate increases. If the domain addresses are the same, the information content of said document is compared with the information content of any one document defined as the reference document.