Perfect Continuous

                                                        Present perfect continuous   

Affirmativect
s.sub.+has+been+m.v.+ing+o.+since/for+time               He has been writing a letter for one hour.
p.sub.+have +been+m.v.+ing+o.                                     We have been writing letters since 2 o'clock.
Negative
s.sub.+has+not+been+m.v.+ing+o.                                  He has not  been writing a letter.
p.sub.+have+not+been+m.v.+ing+o.                           We have not been writing letters since 2 o'clock.
Interrogative
Has+s.sub.+been+m.v.+ing+o.+?                                Has he been writing a letter for one hour?
Have+p.sub.+been+m.v.+ing+o+?                               Have we been writing letters since 2o'clock?
Double Interrogative
Q.word+has+s.sub.+been+m.v.+ing+o.+?            Why has he been writing a letter for one hour?
Q.word+have+p.sub.+been+m.v.+ing+o+?            Why have we been writing letters since 2o'clock?

                                                        Past perfect continuous   

Affirmative 
s.sub.+had+been+m.v.+ing+o.+since/for+time               He had been writing a letter for one hour.
p.sub.+had +been+m.v.+ing+o.since/for+time                    We had been writing letters since 2 o'clock.
Negative
s.sub.+had+not+been+m.v.+ing+o.since/for+time         He had not  been writing a letter for 2 hours.
p.sub.+had+not+been+m.v.+ing+o.since/for+time      We had not been writing letters since 2 o'clock.
Interrogative
Had+s.sub.+been+m.v.+ing+o.+?since/for+time +?         Had he been writing a letter for one hour?
Had+p.sub.+been+m.v.+ing+o+?since/for+time+?          Had we been writing letters since 2o'clock?
Double Interrogative
Q.word+had+s.sub.+been+m.v.+ing+o.+? since/for+time+?
                                                                                        Why had he been writing a letter for one hour?
Q.word+had+p.sub.+been+m.v.+ing+o+?since/for+time+?           
                                                                                   Why had we been writing letters since 2o'clock?

                                                        Future perfect continuous   

Affirmative
s.sub.+will/shall have+been+m.v.+ing+o.+since/for+time
                                                                                    He will have been writing a letter for one hour.
p.sub.+will/shall have +been+m.v.+ing+o. +since/for+time   
                                                                                  We shall have been writing letters since 2 o'clock.
Negative
s.sub.+will/shall+have+not+been+m.v.+ing+o.+since/for+time
                                                                                  He will have not  been writing a letter for 2 hours.
p.sub.+will/shall have+not+been+m.v.+ing+o.+since/for+time
                                                                      We shall have not been writing letters since 2 o'clock.
Interrogative
Will/shall+s.sub.+have+been+m.v.+ing+o.+since/for+time ?
                                                                                 Will he have been writing a letter for one hour?
Will/shall+p.sub.+have+been+m.v.+ing+o+since/for+time ?  
                                                                                   Shall we have been writing letters since 2o'clock?
Double Interrogative
Q.word+will/shall+s.sub.+have+been+m.v.+ing+o.+since/for+time ?       
                                                                     
                                                                            Why will he have been writing a letter for one hour?
Q.word+will/shall+p.sub.+have been+m.v.+ing+o++since/for+time ?           
                                                                         Why shall we have been writing letters since 2o'clock?