Which of the following is a substance formed by the chemical joining of two or more elements in definite amounts?
a. compound
b. isotope
c. nucleus
d. enzyme

"Compound" is the one among the following choices given in the question that is a substance formed by the chemical joining of two or more elements in definite amounts. The correct option among all the options that are given in the question is the first option or option "A". I hope the answer has helped you.

1. true.2. true.3. true.4. false.5. true.the concept of darwin's theory of evolution involves the idea that there are limited resources in a given living environment and that the organisms which live within have variations in their genetic make up due to random mating. the ones with beneficial genetic variations can express certain traits which give them an upper hand in surviving and reproducing in the said environment compared to ones who may have a more disadvantageous variation in traits. over time, the organisms with an upper hand will survive and reproduce more frequently and pass on their beneficial genes while the others die. the result is evolution, where we observe (usually, but not always) eventually, phenotypic distinct changes.