State the null hypothesis for: An experiment testing whether echinacea decreases the length of colds. A correlational study on the relationship between brain size and intelligence. An investigation of whether a self-proclaimed psychic can predict the outcome of a coin flip. A study comparing a drug with a placebo on the amount of pain relief. (A one-tailed test was used.)

The use of echinacea  does not produce changes or increases the duration of colds

Brain size is not correlated with intelligence

The ability of a psychic to predict the results of coin tosses is less than or equal to a random assumption

Explanation:

the answers that were written are referred to the queries made, I separate them into sentences to be even more verbose and to be interpreted better

the answer is c.) there is a warm front in region a and a stationary front in region b.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).