Question

recliners are chairs. people can lean back in them. the first reclining chair was invented in 1790. it was a dentist’s chair. it had a headrest. the dentist could move it. a later dentist added a footrest. the chairs could be adjusted. the patient would lie back while the dentist worked. dentists could raise or lower the chairs. it made their job easier. it made patients more comfortable, too.
the chairs were
○ common
○ small
○ dirty
○ useful

Explanation:

El texto indica que las sillas reclinables para dentistas permitían ajustarse, facilitaban el trabajo de los dentistas y hacían más cómodos a los pacientes, lo que demuestra su utilidad. Las otras opciones (comunes, pequeñas, sucias) no se mencionan en el texto.

Answer:

useful