In order to increase the rate of photosynthesis in a plant, a plant should be developed with many broad leaves. The broad leaves will have increased surface area and more chlorophyll. The increased number of the leaves in the plant will also contribute to the overall increased rate of the photosynthesis.
A strong and thick stalk will support the plant but will have no effect on the rate of photosynthesis. Narrow leaves will decrease the photosynthesis rate. Bright flowers will aid in pollination via the honeybees but not increase the photosynthesis rate.
Hence, the correct answer is 'many broad leaves'.