Physical carrier sensing in 802.11?

I have two questions about IEEE 802.11 MAC protocol.

1) I want to know that physical carrier sense mechanism is adopted for non-RTS packets (CTS, DATA and ACK) or not? For more clarity please consider following scenario:

Suppose that node A sends a RTS packet for node B and node B receives this RTS without collision and also node B is not within a pre-established NAV state. So it should respond to node A by a CTS packet after a SIFS interval. Now suppose that node C which is in node B's transmission range and is not in node A's sensing range (and therefor has not heared RTS of node A) sends a RTS packet during this SIFS interval and so channel will be busy physically for node B, before sending its CTS. In this situation if node B transmits its CTS packet independent of channel busy state or not?

2) Transmission and receiving two packets with time overlap by one node is valid in 802.11 MAC or not? for example in previously described scenario, if node B transmits the CTS, node A can receive it correctly or it will be corrupted because of node C's RTS?

If it is possible for you please solve my confusions.