Final answer:
The two value-based smart bidding strategies are 'Maximize conversion value with target ROAS' and 'Maximize conversion value', both of which prioritize the value of conversions or ROAS.
Step-by-step explanation:
The two types of value-based smart bidding strategies are: c. Maximize conversion value with target ROAS and d. Maximize conversion value. These strategies use machine learning and historical information to optimize bids for conversions or conversion value.
While Target impression share and Manual CPC are other types of bidding strategies, they are not specifically value-based smart bidding strategies. Value-based smart bidding strategies focus on maximizing the value or return on advertising spend (ROAS) considering the value each conversion brings to the business.