Meaning of "plain paper"

[Igor]

English Language Tests, Intermediate level

ESL/EFL Test #229 "Homophone test (12)", question 1

In order to make the training manuals stand out, the company used specialty cardstock rather than ......... paper for the front and back covers.

(a) pane
(b) pain
(c) plain
(d) plane

English Language Tests, Intermediate level

ESL/EFL Test #229 "Homophone test (12)", answer 1

In order to make the training manuals stand out, the company used specialty cardstock rather than plain paper for the front and back covers.

Correct answer: (c) plain
_________________________

please send to me the answer.

Igor

[Yankee]

.
The answer is 'plain':
In order to make the training manuals stand out, the company used specialty cardstock rather than plain paper for the front and back covers.
.