in MS-Excel__________ short cut key is used for hiding rows.

A. Ctrl+H
B. Ctrl+7
C. Ctrl+9
D. None of the above

There are several dedicated keyboard shortcuts to hide and unhide rows and columns.
Ctrl+9 to Hide Rows.
Ctrl+0 (zero) to Hide Columns.
Ctrl+Shift+( to Unhide Rows.
Ctrl+Shift+) to Unhide Columns – If this doesn’t work for you try Alt,O,C,U (old Excel 2003 shortcut that still works).