下列update元素的代码
<set>
<if test="bName != null "> bName=#{bName} ,</if>
<if test="bAuthor != null "> bAuthor=#{bAuthor} ,</if>
</set>
where bId = #{bId}
可以变换成（）？
A.
<trim prefix="SET" suffixOverrides=",">
<if test="bName != null "> bName=#{bName} ,</if>
<if test="bAuthor != null "> bAuthor=#{bAuthor} ,</if>
</trim>
B.
<trim prefix="SET" suffix="WHERE bId = #{bId}">
<if test="bName != null "> bName=#{bName} ,</if>
<if test="bAuthor != null "> bAuthor=#{bAuthor} ,</if>
</trim>
C.
<trim prefix="SET" suffixOverrides="," suffix="WHERE bId = #{bId}">
<if test="bName != null "> bName=#{bName} ,</if>
<if test="bAuthor != null "> bAuthor=#{bAuthor} ,</if>
</trim>
D.
<trim suffixOverrides="," suffix="WHERE bId = #{bId}">
<if test="bName != null "> bName=#{bName} ,</if>
<if test="bAuthor != null "> bAuthor=#{bAuthor} ,</if>
</trim>
正确答案是C