On Machine Learning (Lenear regression and Line of Best fit)

Q. Which one of the following statement is Incorrect?

a. We can make predictions if input values are given and the equation of the line is known.

b. Although it's called Linear regression model,any curve can be used as long as it's fits the data well .

c. In regression models, input and output variables have numerical values.

d. When fitting the line,we are trying to maximize the distance of each point to the line.

(My take: I chose b. But when I look at example of linear regression I do see curves,but they are not steep so I think my answer is wrong.. I assumed that linear regression models only involve straight lines and the data that would form a curve would be outside the model..can you clarify on b.

I saw that they chose D, can you explain why D that's incorrect and kindly elaborate on Fitting the line,I don't quite understand it)