I am working in an assembly file, and I created a new sketch in it which I would like to extrude. I created a block with the sketch, and then I was going to make a part from that block and see if the extrusion options would open up. However, when I go to make a part from the block, it will not let me select the block at all and the "A" (block symbol) is greyed out in the 'selected blocks' window in the "Make Part from Block" property manager. How should I approach this issue so I can extrude the sketch?