Mushfiq Mammadov wrote:1. Question #1, the third sentence:
Maybe a_b should be $ and null should be 0.
Not maybe but definitely

Should be:
a_b defaults to a
0 value.
Mushfiq Mammadov wrote:2. Question #10, the third sentence:
g1 should be g2.
Spot-on! Should be: Reference
one points to
g2 and reference
two is
null.