Only transitive verbs (those that take objects) can be transformed into passive constructions.
Is "A smithy is a blacksmith's workshop." active or passive?-- Active
Is "Most organized religions have monasteries where monks devote their lives to their region." active or passive?-- Active
So if there is only a linking verb, is the sentence active or passive?-- Active
In the sentence "It is a soft-feathered brown bird that reaches a height of up to 6 feet 6 inches.", I know the "is" is a linking verb but is "reaches" an action verb?-- Yes
In the sentence "Although the birds cannot fly, they can travel great distances at speeds over 30 miles per hour.", are fly and travel action verbs-- Yes
and are cannot and can included even though they are only helping verbs?-- No