The correct option is
B The
The sentence indicates that the subjects saw a strange car. Here, 'car' is a singular object. Thus, the answer must be a word that is used along with singular objects.
Option A is incorrect. 'One of' indicates a single choice form multiple objects. Thus, it can only be used with plural objects.
Option B is correct. 'The' is a definite article which can be used for a fixed singular object. Here, there was one fixed car that the subjects so, thus, the object is definite. Therefore, the can be used along with the object and is the correct answer.
Option C is incorrect. 'An' can only be used when the word following it begins with a vowel. Since 'strange' does not begin with a vowel, using 'An' will make the sentence grammatically incorrect.
Option D is incorrect. 'Two' is an adjective of quantity that can only be used for plural objects. Since our object is singular, 'Two' cannot be used.