Please choose the correct ending to complete the given sentence: Education and Communications: [header] How to call an unknown number [title] Listen for single rings. [step] Be suspicious if you hear your phone ring once. A single-ring missed call could be the work of a " crammer ": someone who is trying to get you to call them back so they can charge you.

Ending1: Additionally, if someone calls three times in a row, the operator will want you to ignore the number altogether (not simply ring 4 times). [title] Look to see if the number is about to ring again. Ending2: If you only hear one ring, don't call the number back. If it wasn't a crammer, it was probably a wrong number. Ending3: Be especially wary if you hear the same number twice. [substeps] Instead of interrupting other customers (" hey, chase, hold on ") hear a number while sitting at the table. Ending4: It's a secure line and should not be monitored. If you hear one-ring, that is a good sign.

Answer format: ending1/ending2/ending3/ending4