Question:
Which position did Walford Selby hold in Apr, 1938?

Context:
 Walford Selby holds the position of ambassador of the United Kingdom to Austria from Jan, 1933 to Jan, 1937. 
 Walford Selby holds the position of ambassador of the United Kingdom to Portugal from Jan, 1937 to Jan, 1940. 
 Walford Selby holds the position of Principal Private Secretary to the Secretary of State for Foreign and Commonwealth Affairs from Jan, 1924 to Jan, 1932.

Answer:
ambassador of the United Kingdom to Portugal