By 2050, he _________ (spend) 20 years in prison.
will have spent
What have you eaten today?
CORRECT - unfinished time -- I may even eat more, who knows.
Before my son was born, I'd never been thinking I'd enjoy being a mother
X - I'd never thought I'd enjoy. -- think is a state verb
He ________ (be) in prison for six years before evidence was found that proved his innocence.
had been
You look tired. What did you do?
X - What have you been doing? -- We are interested in the action that caused the result, not if it was completed.
Careful where you put your feet. I've broken a bowl and there is glass everywhere.
CORRECT - a recent action
Her eyes were red and it was clear she had cried.
X - ..."she had been crying" - Perfect Continuous focuses on the action not the completion
She __________ (wait) for her appeal to go to court for over a year.
has been waiting
I noticed a window was broken and the door was open. Someone broke in.
X - "...someone had broken in" - this happened before you noticed the door was open.
This time next year I will have worked here for 10 years.
CORRECT - will have been working - is also possible but focuses on duration not completion
Mark and Tina have dated for six months. They are still going strong.
X - "Mark and Tina have been dating for six months" - focus is on the duration/repetition - not the completed action
Which places had you visited by the time you were 20.
CORRECT -- "by the time" is often used with perfect aspect as it includes the time before you were 20
How many hours had you worked last week?
X- "How many hours did you work last week" - 1. It's specific time - we don't like to use perfect with specific time 2. there is no past simple as an "anchor"
I was exhausted. I was working since 7a.m.
X - "I had been working" -- the action "work" happened before being exhausted and explains why we are tired. Past simple keeps the events in order