Capital letters are used to begin a sentence. Option A begins with a small letter. Hence, this option is incorrect.
The prefix, 'ex' is used before a title to indicate it is a former title i.e a title held earlier and not now. It is to be followed by a hyphen. The letter, 'e' of the prefix, 'ex' is not to be capitalised. In options A, C and D, the letter 'e' is capitalised. There is no hyphen after the prefix 'ex' in all these three options. Hence, all these three options are incorrect.
'MLA' is an acronym for 'Member of the Legislative Assembly'. There is no necessity to put a dot between each letter of an acronym. However, options A, and D have this error.
The word, 'an' is an article. An article in the middle of the sentence should not be capitalised. This error is observed in option C.
The only option without any of the above said errors is option B. This is punctuated correctly. Hence, option B is the correct answer.