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?
1. Past participles are used as part of the present and past perfect tenses (both regular and continuous). The non-continuous present perfect tense uses hasor have + the past participle; the present perfectcontinuous tense uses has or have + been (the pastparticiple of BE) + the-ing form of the main verb. Examples: He has (He's) taken a vacation. /He has (He's) been taking a vacation.