An action in a sentence can be represented in two ways, namely active and passive voice.
The passive voice always uses the past participle form of the main verb irrespective of any tense. Only the auxiliary verbs depend upon the sentence given in the active voice.
The correct answer is A)The fresh flowers are picked every morning by them.
Option A is correct as the given sentence is in the active voice and to transform it into the passive voice, the subject of the given sentence (They) comes in the place of the object (the fresh flowers) and vice versa. Also, as the given sentence is in the simple present tense.
Options B, C, and D are wrong as 'are fresh', 'are picked fresh', and 'picked flowers' cannot be used respectively.