The study of the structure an behaviour of the physical and natural environment by oberseving through scientficic instruments and through experiments.
The answer is A. He seems, however, to have recovered from his fright. While it should have a semi-colon instead of a comma before the "however", it is the only one that is correct. C. needs a comma after "I hope". D. does not use commas but it should have a comma after "rate". B. does not require a comma after "in".
"A. her fearlessness because the dog could kill her" is perhaps the best option from the list, but it should be noted that there are other elements as well.
