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Part $1$

A fundamental distinction between trend projection and linear regression is$$ that:

Part $2$

A$.$

trend projection uses least squares while linear regression does not.

B$.$

in trend projection the independent variable is$$ time; in linear regression the independent variable need not be$$ time, but can be any variable with explanatory power.

C$.$

trend projection uses two smoothing$$ constants, not just one.

D$.$

only linear regression can have a negative slope.

E$.$

trend projection can be a function of several$$ variables, while linear regression can only be a function of one variable.