Which 指代前面的cartoons
cartoons是复数形式,所以make没用第三人称单数.
He is the only one of the doctors in the hospital who has two cars.( 在"one of +名词"结构中,通常名词是先行词；但在one前加the only,则one是先行词,故句子谓语用has.)
特殊：① one of + 复数名词 +关系代词+复数型动词
②the (only) one of + 复数名词+关系代词+单数型动词
比如：
The Great Wall is one of the world-famous buildings that draw lots of visitors.
Titanic is the (only) one of the most wonderful movies that has been
produced in Hollywood.