Choose the appropriate verb form the following : Forty yards ____  a good distance. 

1. "is" - This is the correct choice. Even though 'forty yards' may sound plural because it refers to multiple yards, it actually represents a single measure or unit of distance in this context. When we talk about measurements, time, money, or quantities as a single entity or a collective unit, we use a singular verb. Here, 'forty yards' is considered as one unit of distance, hence the singular verb "is" is used.

2. "are" - This would be incorrect because, as explained above, 'forty yards' is treated as a singular entity in this context.

3. "were" - This is the past tense form and is not appropriate in this sentence, which is in the present tense.

4. "had" - This is also incorrect as it is a form of the past perfect tense and does not fit the present tense construction of the sentence.