Suppose that we use hierarchical clustering to group four observations. The distance between these observations is given in the following table: Observation 1 2 3 4 6 WN 3 1 = 4 7 8 What will be the first two observations grouped: O Observations 1 and 2. O Observations 2 and 3. O Observations 3 and 4. O There is not enough information to determine this. An experiment was conducted to determine the effectiveness of a new drug (as compared to a current drug). Experimental units were split by age into two equally sized groups labelled: 'young' and 'old'. Within each age group, half of the experimental units were randomly assigned to receive the new drug, with the remaining units given the existing drug. The blocking variable(s) is/are: O Age variable. O Drug variable. O Both the age and drug variables. O There are no blocking variables