MY THOUGHTS BELOW: 1(a). The frost has killed the flowers. GOOD 1(b). The flowers have been killed due to the frost. NOT GREAT, BETTER: have died due to the frost 1(c). The flowers have been killed by the frost.GOOD Question: Which is\are grammatically correct? 2(a). Several houses were destroyed by the avalanche. GOOD 2(b). Several houses were destroyed because of the avalanche. OKAY, BUT IMPLIES TO ME THAT THE HOUSES DIED INDIRECTLY BY SOMETHING RELATED TO THE AVALANCHE 2(c). The avalanche destroyed several houses. GOOD Question: Which is\are grammatically correct? 3(a). A holiday by the sea will do you a lot of good. 3(b) A lot of good will be done to you due to a holiday by the sea. MAYBE CORRECT GRAMMATICALLY, BUT A TERRIBLE SENTENCE: VERY AWKWARD. 3(c). You will be done a lot of good by a holiday by the sea. SAME AS 3b, BUT MAYBE EVEN WORSE Question: Which is\are grammatically correct?

I think they are all grammatically ok, but 3b and c are unlikely to be used.