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?
Verbs come in three tenses: past, present, and future. The past is used to describe things that have already happened (e.g., earlier in the day,â¦ Use this quick guide to learn how to use all tenses of a verb properly, including present perfect, past continuous, future perfect continuous, and more.