Sentence Correction

Hi All,

I am facing a problem in understanding the subject of the sentence and associating it with the plural or singular verbs. Here are two eg exemplifying the problem .Please explain ..

６． According to scientists at the University of California, the pattern of changes that have occurred in human DNA over the millennia indicate the possibility that everyone alive today might be descended from a single female ancestor who lived in Africa sometime between 140,000 and 280,000 years ago.
(A) indicate the possibility that everyone alive today might be descended from a single female ancestor who
(B) indicate that everyone alive today might possibly be a descendant of a single female ancestor who had
(C) may indicate that everyone alive today has descended from a single female ancestor who had
(D) indicates that everyone alive today may be a descendant of a single female ancestor who
(E) indicates that everyone alive today might be a descendant from a single female ancestor who

Ans : d
７． A higher interest rate is only one of the factors, albeit an important one, that keeps the housing market from spiraling out of control, like it did earlier in the decade. a) that keeps the housing market from spiraling out of control, like it did earlier in the decade.
b) that keep the housing market from spiraling out of control, as it did earlier in the decade
c) that keeps the housing market from spiraling out of control, as it did earlier in the decade
d) that keep the housing market from spiraling out of control, like earlier in the decade
e) that keep the housing market from spiraling out of control, like it did earlier in the decade

Ans : b

Can you please explain in quest 1 what is the subject Pattern or change ?
and in question 2 whats the subject interest rate /factors ??

Thanks in advance ...