Which of the following statements is true?(a) Van der Waals strain in cis-1,2-dimethylcycl...

Which of the following statements is true?

(a) Van der Waals strain in cis-1,2-dimethylcyclopropane is the principal reason for its decreased stability relative to the trans isomer.

(b) Cyclohexane gives off more heat per group on being burned in air than any other cycloalkane.

(c) The principal source of strain in the boat conformation of cyclohexane is angle strain.

(d) The principal source of strain in the gauche conformation of butane is torsional strain.