def test(steps, a, b):
    # print(a)
    for i,j in steps:
        i-=1
        part = int(a[i:j],3)
        part = bin(part)[2:]
        a=a[:i] + part + a[j:]
        # print(a,i+1,j)
    return a == b

def solve():
    a=input()
    orig_a = a
    b=input()
    if a==b:
        print(0)
        return
    if a=='1' or b=='1':
        print(-1)
        return
    
    # merge end zeros
    i = 0
    while i<len(a) and a[len(a)-1-i] == '0':
        i+=1
    
    steps = []
    if i>1:
        steps.append((len(a)-i+1, len(a)))
        a=a[:-i+1]

    # delete all other zeros
    i = 0
    while i<len(a)-1:
        if a[i]=='0':
            for j in range(i+1,len(a)):
                if a[j]=='1': break
            a = a[:i] + a[j:]
            steps.append((i+1,j+1))
        i+=1

    # either 111s or 111s0
    goal = sum(1 for c in b if c=='1')
    if b[-1] == '1': # need to remove trailing, add 1 later
        goal-=1

    # put in trailing 0
    if a[-1] == '1':
        steps.append((len(a)-1,len(a)))
        a=a[:-1] + '00'
        steps.append((len(a)-1,len(a)))
        a=a[:-1]

    # add
    cur = sum(1 for c in a if c=='1')
    while cur < goal:
        steps.append((len(a)-1,len(a)))
        a=a[:-1] + '1'
        steps.append((len(a)-1,len(a)))
        a=a[:-1] + '00'
        steps.append((len(a)-2,len(a)-1))
        a=a[:-2] + '10'
        cur+=1

    # delete
    while cur > goal:
        steps.append((len(a)-2,len(a)-1))
        a=a[:-2] + '000'
        steps.append((len(a)-2,len(a)))
        a=a[:-2]
        cur-=1

    if b[-1] == '1':
        steps.append((len(a)-1,len(a)))
        a=a[:-1]+'1'

    # now we have correct number of ones
    
    # trailing zeros
    goal = 0
    while goal<len(b) and b[-1-goal]=='0': goal+=1

    rem = ''
    if goal:
        cur = 1
        while cur < goal:
            steps.append((len(a)-1,len(a)))
            # a=a[:-1] + '1'
            steps.append((len(a)-1,len(a)))
            # a=a[:-1] + '0' # + another '0'!!
            # rem = '0'+rem
            cur+=1

    # mid zeros
    i = 0
    while i<len(b):
        j=i+1
        while j<len(b):
            if b[j]=='1':
                break
            j+=1
        if j == len(b):
            break
        num_zeros = j-i-1


        if num_zeros:
            # add 2 zeros
            steps.append((i+1,i+2))
            steps.append((i+1,i+3))

            if num_zeros == 1:
                steps.append((i+3,i+4))
            else:
                for _ in range(num_zeros-2):
                    steps.append((i+1,i+2))
                    steps.append((i+1,i+2))

        i=j
    
    if not test(steps, orig_a, b):
        exit(1)

    print(len(steps))
    for s in steps:print(*s)

for _ in range(int(input())):
    solve()
    # break