Which organ is responsible for training T-cells?

tonsils
appendix
spleen
thymus

Below, the levels of organization in a multicellular organism are shown from least to most complex. which level of organization can be described as several different types of tissues working together to perform a common task?

Which of these is most likely to happen if parallax measurements of star distances are taken after a gap of six months? the results would be accurate the results would be inconsistent the results would not be valid the results would not be repeated

Which feature of a human community is similar to a niche in a biological community