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?
(main verb: written ; auxiliary verb: had) We had been stranded for six days. (main verb: been ; auxiliary verb: had) In Spanish, the past perfect tense is formed by using the imperfect tense of the auxiliary verb âhaberâ with the past participle. You have already learned in a previous lesson that the past participle is formed by dropping the infinitive ending and adding either -ado or -ido.