The DateTime.ParseExact method converts a string into a DateTime object using a specified format and culture1. The format parameter defines the order and symbols of the date and time components in the string2. The culture parameter determines the conventions for date separators, time indicators, and other symbols3.

In this case, the string variable DateString has the value “03/03/2023 16:23:11”, which means the 3rd of March, 2023, at 4:23:11 PM. To convert this string into a DateTime variable, we need to use the format “dd/MM/yyyy HH:mm:ss”, which matches the order and symbols of the string components. The “dd” represents the day as two digits, the “MM” represents the month as two digits, the “yyyy” represents the year as four digits, the “HH” represents the hour as two digits in 24-hour format, the “mm” represents the minute as two digits, and the “ss” represents the second as two digits2. The slashes (“/”) and colons (“:”) are used as date and time separators respectively. The Culturelnfo.InvariantCulture parameter specifies that the string uses invariant culture, which means it is not associated with any specific language or region3.

Therefore, option D is the correct expression to convert the string variable DateString into a DateTime variable. Option A has a wrong hour format (“hh” instead of “HH”), which would cause an exception if the hour is greater than 12. Option B has a wrong order of day and month (“MM/dd” instead of “dd/MM”), which would result in an incorrect date. Option C has a wrong minute format (“mm” instead of “MM”), which would cause an exception if the month is greater than 12.