Which question cannot be answered scientifically because the quantity cannot actually be measured?

Which of the following produces carbon dioxide? a. plants b. animals c. decomposers d. all of the above

Use the phylogenetic tree to the right to determine which statement below is true. organisms a and f are not related. organism e is more closely related to organism b than organism f. organisms c and d are more closely related than organisms a and b. phylogenetic trees

Ascientific idea becomes valid when it is what?