Concept:
Masitkhani Gat is an important instrumental composition, especially in sitar playing.
It is generally played in Vilambit laya and is commonly set in Trital.
Step 1: Check statement A.
Masitkhani Gat is generally set to Trital.
So, A is correct.
Step 2: Check statement B.
Its bols are fixed in a traditional pattern.
So, B is correct.
Step 3: Check statement C.
The statement that the Mukhra starts from the 7th matra is not accepted as a general characteristic here.
So, C is incorrect.
Step 4: Check statement D.
Masitkhani Gat is performed in Vilambit laya.
So, D is correct.
Step 5: Final conclusion.
The correct statements are:
\[
A,\ B,\ D
\]
Hence:
\[
\boxed{\text{(B) A, B and D only}}
\]