Which could cause waits on the db file sequential read event?

Examine the following information from the AWR report:
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event Waits Time (s) Call Time
————————————– ———— ———– ———
CPU time 559 88.80
log file parallel write 2,181 28 4.42
SQL*Net more data from client 516,611 27 4.24
db file parallel write 13,383 13 2.04
db file sequential read 563 2 .27
Which could cause waits on the db file sequential read event?

A.
too many full table scans

B.
too large a database buffer cache

C.
too many waits occurring while reading multiple blocks synchronously

D.
toomany index range scans occurring which refers to blocks not in the database buffer cache