Question 697531
Discrete variables are ones that can only have certain values i.e.think about people, you can have any whole number(integer) of people but you cannot have 3.2 people. 
Continuous variables are ones that are measured on a sliding scale and can take (almost) any value, i.e. think about temperatures, you can have temperatures of 20degrees, 174.55degrees or if you have a very accurate thermometer you could measure to any number of decimal places.
A is a discrete variable as you can only have integer values of people.
B is continuous as time can be measured in minutes, seconds and fractions of seconds.
C is also continuous as you can measure blood pressure on a sliding scale.
D is a discrete variable (see explanation for A above)