Supply the sentences with the correct alternative:
I. This is the hardest problem _____ I have ever had to face.
II. A doctor, _____ patients trust him, has great responsibility.
III. Vesuvius, _____ is a lofty volcano, overlooks the Bay of Naples.
IV. My friend Marcello, _____ is in hospital, is very ill.
V. There's something _____ I must tell you in confidence.

Alternativas -
a) I. that; II. which; III. what; IV. who; V. that
b) I. which; II. whose; III. that; IV. whose; V. which
c) I. that; II. whose; III. which; IV. who; V. that
d) I. what; II. who; III. which; IV. that; V. what
e) I. that; II. whose; III. what; IV. which; V. that