Here are the practice examples
(A) The weight of bags of apples, with 20 apples in a bag (B) The number of times required for a modem to dial an internet provider before connecting (C) A pair of dice is rolled, and the sum to appear on the dice is recorded (D) The time it takes to complete an exercise session
A is continuous because the weight can be anything within a certain range. B is discrete because the number can be 1, 2, 3, ... but it cannot be in-between values like 1·7. C is discrete because the sum can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. D is continuous because the time can be any positive real number.
With A and D, if you gave me two possible values for the variable, I could always give you another value, in between those two, which would also be a possible value for the variable. This would not be true for B and C.
I hope this helps