computer networks – 802.11 WLAN transmissions

If we have three WiFi devices A,B,C in a 802.11 WLAN. Both A and B have frames to sent to C and can hear C’s transmissions. Which of the following scenarios will results in collisions? DIFS = 2xslot_ + SIFS. Multiple can apply

1.) A and B are hidden terminals to each other. At time t0, A starts a backoff timer of 2 slots. B just arrives to the network

2.) A and B are hidden terminals to each other. At time t0, A just successfully sent a frame to C and is waiting for the acknowledge frame from C (A has no more frame to send); B has a backoff timer of 1 and a frame to send to C.

3.) A and B can hear each other’s transmissions. Both A and B have frames to send to C. At time t0, A starts a backoff time of 2 slots. B just arrives to the network.

4.) A and B can hear each other’s transmissions. At time t0, A just successfully sent a frame to C and is waiting for an acknowledge frame from C (A has no more frame to send); B has a backoff timer of 1 and a frame to send to C.

I believe the answer is 1 and 3 as I don’t think according to 802.11 2 and 4 make any sense. Could someone verify these please?