When D-galactose was heated at 165C, a small amount of compound A was isolated: The structure of

Question:

When D-galactose was heated at 165°C, a small amount of compound A was isolated:

The structure of compound A was established, in part, by converting it to known compounds. Treatment of A with excess methyl iodide in the presence of silver oxide, followed by hydrolysis with dilute hydrochloric acid, gave a trimethyl ether of D-galactose. Comparing this trimethyl ether with known trimethyl ethers of D-galactose allowed the structure of compound A to be deduced.
How many trimethyl ethers of D-galactose are there? Which one is the same as the product
derived from compound A?