Quote:
Augustus DeMorgan made many valuable contributions to calculus, trigonometry, algebra, and logic; but perhaps his most famous academic contribution, a pair of theorems concerning complementation of sets, is still known today as DeMorgan’s Rules.
a.a pair of theorems concerning complementation of sets, is
b.a pair of theorems concerning complementation of sets, are
c.two theorems that have to do with complementation of sets, are
d.two theorems that define complementation of sets, is
e.two theorems that are both related to complementation of sets, are
Subject-verb combination quickly eliminated B, C and E due to plural verb
are.
Coming to A and D, both are different in meaning.
Quote:
Concern means Relate to;
the story concerns a friend of mine
(be concerned with) this fable is concerned with forgiveness and redemption
MORE EXAMPLE SENTENCES
Of course, the Today Tonight story was only concerned with the latter issue.
Julian Barnes's new book of short stories is concerned with old age and death.
View synonyms
involved, affected; connected, related, implicated
a pair of theorems related to complementation of sets is not the same as
two theorems that define complementation of sets since we do not know whether theorems are just related to the complementation of sets or they define complementation of sets.
We cannot assume so go for A.