I have a directory where there are multiple folders, each of folder contains a .gz file.
How can I unzip all of them at once?

My data looks like this

List of folders

    A
    B
    C
    D

In every of them there is file as

    A
    a.out.gz
    B
    b.out.gz
    C
    c.out.gz
    D
    d.out.gz