bharti.2010 wrote:While crocuses, when ingested, are poisonous and induce severe vomiting in some people, they are often fatal to others, whose immune systems are weakened by liver complications.

(A) they are often fatal to others, whose
(B) they are often fatal to others in that their
(C) for others, they are often fatal because their
(D) for some, it is often fatal in that their
(E) it can often be fatal to others, whose

B & C - 'their' in both the options doesn't have a clear referent.
D & E - 'it' is wrong - they should be used for plural crocuses.

IMO A.

P.S: Please underline the part under study.

While crocuses, when ingested, are poisonous and induce severe vomiting in some people, they are often fatal to others, whose immune systems are weakened by liver complications.

(A) they are often fatal to others, whose
(B) they are often fatal to others in that their
(C) for others, they are often fatal because their
(D) for some, it is often fatal in that their
(E) it can often be fatal to others, whose

FIRST, PLS UNDERLINE THE PART OF THE SENTENCE UNDER STUDY!

IMO:A