患儿男，8岁。因呕血、黑便1天入院。既往有类似呕血史2次，发现乙肝大三阳5年。查体：重度贫血貌，面色苍白，肢端凉，心率120次／分，血压85/60mmHg，腹部平软，中上腹轻压痛，肝肋下未触及，脾肋下2cm。

该患儿消化道出血的原因是（）

A.急性胃炎

B.消化性溃疡

C.慢性胃炎

D.食管静脉曲张

E.过敏性紫癜

Occasions are quite rare _____ the father has the time to spend a day with his kids. [ ]

A. when

B. which

C. why

D. that