Confusion in the DCAP process

[aghia98]

Hi,
I am reading the Intel's documentation and third party papers to undrstand the DCAP protocol and I am bit confused in some steps.

1. What is the difference between the attestation key (AK) and the provisioning certification key (PCK) ? The former is used to sign enclave quotes while the second is used to sign QE Reports and authenticate the former...Why not only the PCK is used then ?
2. What is the difference between a quote and a QE report ?
3. To check the enclave, Intel provides quote verification enclave (QvE)... Why do we need an enclave to check the quotes since the protocol exposes the certification chain and anyone can check it ?

thank you in advance