Approximately 8,000 years ago, changes in occurred as humans chose plants that did not and therefore held seeds on the plant making it easier to harvest the grain.

Approximately 8,000 years ago, changes in wheat occurred as humans chose plants that did not shatter and therefore held seeds on the plant making it easier to harvest the grain.

Explanation:

8000 years ago when wheat mature, some varieties shatter and maturity while others keep their wheat spikes intact. Shattering in wheat is an undesirable process in agriculture as it makes harvesting more difficult. Over the millenia, humans decided to plant only wheat that hold their seeds at maturity and do not shatter as this make it easier to harvest the grain. This led to a reduction in the number of wheat varieties that shatter.

angle a = 40.6°

step-by-step explanation:

for any right angle triangle we know the pythagoras theorem reveals

hypotenuse² = height²+base²

by this formula we will calculate the length of hypotenuse

h² = 6²+7²

⇒ h =√36+49 = √85 = 9.22

now from the given triangle sin a = height/ hypotenuse

                                                sin a = 6/9.22 = 0.651

therefore

so angle a = 40.6°