What is the reason why Spain sponsored the first voyage of Columbus to the west

Donald is studying the eating habits of all students attending his school. he samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. he then collects data from the sample. which type of sampling is used? select the correct answer below: systematic sampling convenience sampling stratified sampling cluster sampling

The form the boundary between north and south china. a. himalayan mountains c. change river b. xi river d. qinling shandi mountains

True or false? correlations can only be negative.