If corn basis today is $+40$ Dec $(40$ cents over December futures$)$ and in two months' time it is $+20$ Dec $(20$ cents over December futures$),$ which of the following statements is true?

Basis weakened $20$ cents per bushel over the two months

Basis strengthened $20$ cents per bushel over the two months

Basis weakened $40$ cents per bushel over the two months

Basis strengthened $40$ cents per bushel over the two months