<p style="">In the sentence "All sales clerks are asked ______ in a customer relations workshop...", the phrase "are asked" is in the passive voice. In the passive voice, the subject ("All sales clerks") is the receiver of the action. The doer of the action (i.e., who is doing the asking) is not specified, which is common in passive constructions.</p><p style="">In an active voice, the subject does the action: "The company asks the sales clerks to <span class="highlight">.....</span>.".</p><p style="">In a passive voice, the action is done to the subject: "The sales clerks are asked to ....".</p><p style="">You can see that "to" is still in the passive voice. So, the answer is (c) to participate.</p><p style="">The sentence becomes: </p><p style=""><strong>All sales clerks are asked to participate in a customer relations workshop, which will be held on August 14 at 3 P.M.</strong></p><p style="">In summary, when using the passive voice like "are asked," we often follow it with "to" + verb to indicate what action is being requested.</p>