The correct pairs are AF, BE, and CD. AF - The main verb START in E can come after the modal verb MUST given in A to convey that according to the principles of corporate management stress, transitions should start from the top, but the real changes should happen at the bottom. "The principles of corporate change management stress that, although transitions must start at the top, the real change needs to happen at the bottom." BE - The noun phrase CLEANER SOURCES OF ENERGY in E can act as the object of the preposition TOWARDS given in B. The sentence here seeks to convey that in the long term, the benefits of shifting away from fossil fuels to cleaner energy sources will be much greater than the costs involved in the process. "In the long term, the benefits for humanity of a societal shift away from fossil fuels and towards cleaner sources of energy will far outweigh the costs. " CD - The adjective GREAT in sentence C needs to modify a noun. STRIDES given in D will be a suitable match here. The sentence seeks to convey that investments in renewable energy are making significant progress along with the rapidly dropping costs of wind and solar energy. "Investment in renewable energy is making great strides and the cost of wind and solar energy is falling fast." Thus, B is the right answer.