The acceleration of the universe's expansion is attributed by many cosmologists to the presence of which of the following?

a. dark matter
b. black holes
c. dark energy
d. gravitaional pulls from unseen galaxies**
i think its d but not sure

Beryl states that insulation with the smallest possible thermal conductivity is best to keep a house warm in winter, but worst for keeping a house cool in summer. sapphire insists the reverse is true: low thermal conductivity is good in the summer, but bad in the winter. which one, if either is correct? a. beryl, because low thermal conductivity results in low heat transfer. b. beryl, because low thermal conductivity results in high heat transfer. d. sapphire, because low thermal conductivity results in high heat transfer. e. neither, because low heat transfer is desirable both in summer and in winter.