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?
We use the Past Perfect tense to emphasize that an action in the past finished before another action in the past started.se 1: A completed action before another action in the past. The first use of this tense is to emphasize that one action in the past happened before another action in the past. 1  I. 2  my homework before I went playing football.