那位校长在这次访问中的所见所闻给他留下了深刻的印象。
A、 What the principal saw and heard during his visit gave him a deep impression.
B、 That the principal saw and heard during his visit gave him a deep impression.
C、 Which the principal saw and heard during his visit gave him a deep impression.
D、 All the principal saw and heard during his visit gave him a deep impression.