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 can be used in other forms, such as the present progressive, but in grammar treatises that is not usually considered a special tense but rather one of the periphrastic verbal constructions. In Old Spanish there were two tenses (simple and compound future subjunctive) that are virtually obsolete today. Perfect: In Spanish, verbs that are conjugated with haber (to have [done something]) are in the perfect aspect. 2  Perfective: In Spanish, verbs in the preterite are in the perfective aspect. 3  Imperfective: In Spanish, the present, imperfect, and future tenses are in the imperfective aspect.