Use the data in BARIUM for this exercise.$($i$)$ Add a linear time trend to equation $(10\mathrm{.}22)($refer to equation $10\mathrm{.}22$ pg $350$ in the text book$).$ Are any variables, other than the trend, statistically significant?

a$.$

The variable afdec$6$ is significant in addition to the trend

b$.$

Both afdec$6$ and befile$6$ are significant with the trend

c$.$

all the included variables are significant

d$.$

Only the trend is statistically significant