could throb
Regular verb: throb - throbbed- throbbed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could throb
you could throb
he could throb
we could throb
you could throb
they could throb 	I could be throbbing
you could be throbbing
he could be throbbing
we could be throbbing
you could be throbbing
they could be throbbing	I could have throbbed
you could have throbbed
he could have throbbed
we could have throbbed
you could have throbbed
they could have throbbed	I could have been throbbing
you could have been throbbing
he could have been throbbing
we could have been throbbing
you could have been throbbing
they could have been throbbing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't throb
you couldn't throb
he couldn't throb
we couldn't throb
you couldn't throb
they couldn't throb 	I couldn't be throbbing
you couldn't be throbbing
he couldn't be throbbing
we couldn't be throbbing
you couldn't be throbbing
they couldn't be throbbing	I couldn't have throbbed
you couldn't have throbbed
he couldn't have throbbed
we couldn't have throbbed
you couldn't have throbbed
they couldn't have throbbed	I couldn't have been throbbing
you couldn't have been throbbing
he couldn't have been throbbing
we couldn't have been throbbing
you couldn't have been throbbing
they couldn't have been throbbing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I throb?
could you throb?
could he throb?
could we throb?
could you throb?
could they throb? 	could I be throbbing?
could you be throbbing?
could he be throbbing?
could we be throbbing?
could you be throbbing?
could they be throbbing? 	could I have throbbed?
could you have throbbed?
could he have throbbed?
could we have throbbed?
could you have throbbed?
could they have throbbed? 	could I have been throbbing?
could you have been throbbing?
could he have been throbbing?
could we have been throbbing?
could you have been throbbing?
could they have been throbbing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I throb?
couldn't you throb?
couldn't he throb?
couldn't we throb?
couldn't you throb?
couldn't they throb? 	couldn't I be throbbing?
couldn't you be throbbing?
couldn't he be throbbing?
couldn't we be throbbing?
couldn't you be throbbing?
couldn't they be throbbing? 	couldn't I have throbbed?
couldn't you have throbbed?
couldn't he have throbbed?
couldn't we have throbbed?
couldn't you have throbbed?
couldn't they have throbbed? 	couldn't I have been throbbing?
couldn't you have been throbbing?
couldn't he have been throbbing?
couldn't we have been throbbing?
couldn't you have been throbbing?
couldn't they have been throbbing?