I can trek you can trek he can trek we can trek you can trek they can trek
V-ing form
I can be trekking you can be trekking he can be trekking we can be trekking you can be trekking they can be trekking
Perfect
I can have trekked you can have trekked he can have trekked we can have trekked you can have trekked they can have trekked
V-ing perfect
I can have been trekking you can have been trekking he can have been trekking we can have been trekking you can have been trekking they can have been trekking
Negation
Simple form
I can't trek you can't trek he can't trek we can't trek you can't trek they can't trek
V-ing form
I can't be trekking you can't be trekking he can't be trekking we can't be trekking you can't be trekking they can't be trekking
Perfect
I can't have trekked you can't have trekked he can't have trekked we can't have trekked you can't have trekked they can't have trekked
V-ing perfect
I can't have been trekking you can't have been trekking he can't have been trekking we can't have been trekking you can't have been trekking they can't have been trekking
Interrogative form
Simple form
can I trek? can you trek? can he trek? can we trek? can you trek? can they trek?
V-ing form
can I be trekking? can you be trekking? can he be trekking? can we be trekking? can you be trekking? can they be trekking?
Perfect
can I have trekked? can you have trekked? can he have trekked? can we have trekked? can you have trekked? can they have trekked?
V-ing perfect
can I have been trekking? can you have been trekking? can he have been trekking? can we have been trekking? can you have been trekking? can they have been trekking?
Interro-negative form
Simple form
can't I trek? can't you trek? can't he trek? can't we trek? can't you trek? can't they trek?
V-ing form
can't I be trekking? can't you be trekking? can't he be trekking? can't we be trekking? can't you be trekking? can't they be trekking?
Perfect
can't I have trekked? can't you have trekked? can't he have trekked? can't we have trekked? can't you have trekked? can't they have trekked?
V-ing perfect
can't I have been trekking? can't you have been trekking? can't he have been trekking? can't we have been trekking? can't you have been trekking? can't they have been trekking?