End face mechanical seal - Seal categories. 1  All mechanical seals must contain the four elements described above but the way those functional elements are arranged may be quite varied. 2  Mechanical seals are generally classified into two main categories: Pusher or Non-Pusher.
User: Which verb form is used to indicate present perfect tense? verb or verb-s will verb have verb-ed have verb-ingWeegy: The verb form is used to indicate the perfect progressive tense is: have + been + verb + -ing weegy2x|Points 179|User: Which statement about a letter of complaint is true?
Present Perfect Tense. Present perfect tense describes an action that happened at an indefinite time in the past or that began in the past and continues in the present.This tense is formed by using has / have with the past participle of the verb.ast Perfect Progressive. Past perfect progressive tense describes a past, ongoing action that was completed before some other past action. This tense is formed by using had been and the present perfect of the verb (the verb form ending in-ing).