The best answer is b - vascular bundles arranged in a ring.
Vascular bundles in dicots are fewer and are arranged in circle or rings.
Other differences include;
1. dicots have tap root system while monocots have adventitious root system.
2. Dicots have flowers arranged in multiples of five while in monocots, they are in multiples of three.
3. Dicot stem is usually solid while the monocot stem is usually hollow.
4. Dicots have cambium and secondary growth in stem while monocots have no cambium and no secondary growth in stem
