English verb conjugation
COULD SNIFF

Regular verb: sniff - sniffed - sniffed

Affirmation

Simple form	V-ing form
I could sniff you could sniff he could sniff we could sniff you could sniff they could sniff	I could be sniffing you could be sniffing he could be sniffing we could be sniffing you could be sniffing they could be sniffing
Perfect	V-ing perfect
I could have sniffed you could have sniffed he could have sniffed we could have sniffed you could have sniffed they could have sniffed	I could have been sniffing you could have been sniffing he could have been sniffing we could have been sniffing you could have been sniffing they could have been sniffing

Negation

Simple form	V-ing form
I couldn't sniff you couldn't sniff he couldn't sniff we couldn't sniff you couldn't sniff they couldn't sniff	I couldn't be sniffing you couldn't be sniffing he couldn't be sniffing we couldn't be sniffing you couldn't be sniffing they couldn't be sniffing
Perfect	V-ing perfect
I couldn't have sniffed you couldn't have sniffed he couldn't have sniffed we couldn't have sniffed you couldn't have sniffed they couldn't have sniffed	I couldn't have been sniffing you couldn't have been sniffing he couldn't have been sniffing we couldn't have been sniffing you couldn't have been sniffing they couldn't have been sniffing

Interrogative form

Simple form	V-ing form
could I sniff? could you sniff? could he sniff? could we sniff? could you sniff? could they sniff?	could I be sniffing? could you be sniffing? could he be sniffing? could we be sniffing? could you be sniffing? could they be sniffing?
Perfect	V-ing perfect
could I have sniffed? could you have sniffed? could he have sniffed? could we have sniffed? could you have sniffed? could they have sniffed?	could I have been sniffing? could you have been sniffing? could he have been sniffing? could we have been sniffing? could you have been sniffing? could they have been sniffing?

Interro-negative form

Simple form	V-ing form
couldn't I sniff? couldn't you sniff? couldn't he sniff? couldn't we sniff? couldn't you sniff? couldn't they sniff?	couldn't I be sniffing? couldn't you be sniffing? couldn't he be sniffing? couldn't we be sniffing? couldn't you be sniffing? couldn't they be sniffing?
Perfect	V-ing perfect
couldn't I have sniffed? couldn't you have sniffed? couldn't he have sniffed? couldn't we have sniffed? couldn't you have sniffed? couldn't they have sniffed?	couldn't I have been sniffing? couldn't you have been sniffing? couldn't he have been sniffing? couldn't we have been sniffing? couldn't you have been sniffing? couldn't they have been sniffing?