They have decided to send a spaceship.. (as main verb?)X
They have done tests and know that plants can grow there (as an aux verb?)
They have not seen any alien life there (as an aux verb?)
'have' in the first sentence performs exactly the same function as in the first - an auxiliary used to form the present perfect.
The next group is 'be' as a main and auxiliary verb
No one else will be able to join the space colony. what do you think?
The spaceship will be controlled from Earth (be as aux verb since will is a modal verb and controlled would be the main verb?) 'be' is an auxiliary verb used to form the passive.
They are very confident that human beings will be able to live there what do you think?
They have not seen any alien life there, but they cannot be sure that it doesn't exist (be as main verb?)
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