Which of the following best describes a centric holding cusp of a mandibular left second molar?
a. it is the distofacial cusp and occludes in the embrasure between maxillary first and second molars.
b. it is the distofacial cusp and occludes in the central fossa of a maxillary second molar.
c. it is the distolingual cusp and occludes in the embrasure between maxillary first and second molars.
d. it is the distolingual cusp and occludes in the central fossa of a maxillary second molar.

You are studying several alleles of an e. coli helicase gene. one allele, called rsr, confers resistance to rs2014, an antibiotic that works by inhibiting helicase activity. bacteria with the rss allele are sensitive to rs2014. another allele, called ts-, produces a temperature sensitive mutation of the helicase. in bacteria with the ts- allele, helicase is inactivated at 42 °c but functions normally at 37 °c. helicase functions normally at both temperatures in bacteria with the ts allele. you obtain the following data while testing four strains of e. coli at different temperatures and doses of rs2014. each number represents the percentage of maximal dna synthesis. based on this data, assign the appropriate genotype to strains a–d in the spaces provided