Donald Trump unable to attend Republic Day parade

US President Donald Trump will be unable to attend the Republic Day parade on Prime Minister Narendra Modi's invitation because of "scheduling constraints", the White House 

has said but stressed the "strong personal rapport" shared by the two leaders.

• No explanation was offered but the Republic Day parade on January 26 is around the time when US presidents usually present their annual report to the Congress, a statement of achievements of the past year and plans for the next, called the State of the Union address.

Interesting to know:

• Barack Obama, who became the first American president to attend the Republic Day parade in 2015, had moved up his address to January 20 from the usual end-of-month slot he had favoured thus far. 
• But it was not clear if Trump's "scheduling constraints" included the address.
• A spokesperson from the White House stressed the personal rapport shared by the leaders, possibly to prevent the US' decision from being spun as a snub, as it might be given recent tensions in ties over trade and American threats of sanctions for buying Russian defence equipment and crude oil from long-time supplier Iran.

About the Invitation:

• The Indian invitation to Trump was never made public. 
• It was extended quietly as something that is called a "pre-invitation" among diplomats, an opening move to gauge the mood of the guest. 
• If the response seems positive and both parties are certain of an acceptance, a formal invitation follows.
• "A quiet pre-invitation ensures neither party- especially the host- is embarrassed and feels snubbed if the visit is not likely to work out," a former White House official involved with several presidential visits said on background.

Question:

Q. Who will be unable to attend the Republic Day parade on Prime Minister Narendra Modi's invitation because of "scheduling constraints"?
a. US President Donald Trump
b. French President Emmanuel Macron
c. German Chancellor Angela Merkel
d. None of the above