This happens quite a lot in verbs e.g run to running. It is because you double the last consonant in a one-syllable noun for it to become a verb. (Keep in mind there are exceptions to this rule.)
he created laws because there we no laws in the old years
For 5 C and D could work
For 6 it is D
For 7 is A
And 8 is D
"Martha" is a proper noun and "cat" is a common noun.