99B- A319 is correct
which means the entire answer is UA, YYZ-ORD A319, ORD-SFO 747-100/200, SFO-MFR 737-300


as for your other guesses ... sorry, I keep editing stuff in the wrong places on my phone late at night

99D- the late evening itinerary (that actually arrives mid-morning on Saturday) includes three airlines and one regional aircraft
what we know so far: the 744 is not on the first segment, is not a Combi (74E), and does not belong to either AC or KE; the first connecting point is not YVR or ANC or JFK; the second leg is not on DL or AS, or a 737 of any type
HINT: the 747 is on the longest of the three segments; the other mainline flight is on an aircraft that also appears in one of the other routings

LY is incorrect
LAX is incorrect
M80 is incorrect

and for the remaining one --
99C- the midafternoon itinerary is on two airlines and involves one regional aircraft
what we know so far: the 747 is a -200 Combi (74M); the first connecting point is not DTW; the second leg XXX-PDX is on a 757, not NW
HINT: the 747 is NOT on the longest of the three segments