【不定式作表语】
1.说明主语的具体内容.
如：Mary'task is to set the table.
2.表其他如目的.
如：This wall is to keep people out of the garden.
【现在分词作表语】
1.某些现在分词已变作形容词可作表语.（如表情绪的词.）
如：He was very amusing.
2.表状态、品质的现在分词可用作表语.
如：She is always very obliging.
祝开心!